Rigidbody character controller issues

I'm working on a character controller, everything works fine except two things and I can't find a way to solve this :( This is the code of my controller script :

 using UnityEngine;
 
 public class ControlsManager : MonoBehaviour
 {
     public Transform playerBody;
     private Rigidbody _rigidbody;
 
     private Transform _playerCamera;
 
     private Vector2 _mousePosition;
     private Vector2 _precMousePosition;
     private float _rJoystickX;
     private float _rJoystickY;
 
     private float _sprint;
     private bool _jump;
 
     private Vector3 _bodyTranslation;
     private bool _bodyTranslationChange;
     private Vector3 _bodyRotation;
     private bool _bodyRotationChange;
     private Vector3 _cameraRotation;
     private bool _cameraRotationChange;
 
 
     private void Awake()
     {
         _rigidbody = playerBody.GetComponent<Rigidbody>();
         _playerCamera = Utilities.mainCamera.transform;
         _mousePosition = Input.mousePosition;
     }
 
     private void Update()
     {
         _sprint = 1;
 
         // Cursor lock for camera rotation
         if (Input.GetKeyDown(Utilities.controls.lockCursorMouse))
         {
             if (Cursor.lockState == CursorLockMode.None)
             {
                 Cursor.visible = false;
                 Cursor.lockState = CursorLockMode.Locked;
             }
             else
             {
                 Cursor.visible = true;
                 Cursor.lockState = CursorLockMode.None;
             }
         }
 
 
         if (!Utilities.isGamePaused)
         {
 
             if (Input.GetJoystickNames().Length > 0 && Input.GetJoystickNames()[0] != "")
             {
                 // Camera rotation for controller
                 _rJoystickX = Input.GetAxis("RJoystickX");
                 _rJoystickY = Input.GetAxis("RJoystickY");
 
                 if (_rJoystickX != 0) {
                     _bodyRotation.y += Utilities.controls.controllerSens * _rJoystickX * Time.deltaTime;
                     _bodyRotationChange = true;
                 }
                 if (_rJoystickY != 0)
                 {
                     _cameraRotation.x += Utilities.controls.controllerSens * _rJoystickY * Time.deltaTime;
                     _cameraRotationChange = true;
                 }
 
                 // Movements for controller
                 if(Input.GetKey(Utilities.controls.sprintController))
                 {
                     _sprint = 1.6f;
                 }
 
                 if (Input.GetAxis("LJoystickY") > 0)
                 {
                     _bodyTranslation += playerBody.forward * _sprint * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
                 if (Input.GetAxis("LJoystickY") < 0)
                 {
                     _bodyTranslation -= playerBody.forward * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
                 if (Input.GetAxis("LJoystickX") < 0)
                 {
                     _bodyTranslation -= playerBody.right * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
                 if (Input.GetAxis("LJoystickX") > 0)
                 {
                     _bodyTranslation += playerBody.right * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
             }
 
 
             if (Cursor.lockState == CursorLockMode.Locked)
             {
                 // Camera rotation for mouse
                 _precMousePosition = _mousePosition;
                 _mousePosition.x = Input.GetAxis("Mouse X");
                 _mousePosition.y = Input.GetAxis("Mouse Y");
 
                 if (_mousePosition.x != _precMousePosition.x)
                 {
                     _bodyRotation.y += _mousePosition.x * Utilities.controls.mouseSens;
                     _bodyRotationChange = true;
                 }
                 if (_mousePosition.y != _precMousePosition.y)
                 {
                     _cameraRotation.x += -_mousePosition.y * Utilities.controls.mouseSens;
                     _cameraRotationChange = true;
                 }
 
                 // Movements for mouse
 
                 _sprint = 1;
                 if(Input.GetKey(KeyCode.LeftShift))
                 {
                     _sprint = 1.6f;
                 }
 
                 if (Input.GetKeyDown(KeyCode.Space))
                 {
                     _jump = true;
                 }
 
                 if (Input.GetKey(Utilities.controls.forward))
                 {
                     _bodyTranslation += playerBody.forward * (_sprint * Time.deltaTime);
                     _bodyTranslationChange = true;
                 }
                 if (Input.GetKey(Utilities.controls.backward))
                 {
                     _bodyTranslation -= playerBody.forward * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
                 if (Input.GetKey(Utilities.controls.left))
                 {
                     _bodyTranslation -= playerBody.right * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
                 if (Input.GetKey(Utilities.controls.right))
                 {
                     _bodyTranslation += playerBody.right * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
 
                 ///////////////////////////////// Debug
                 if (Input.GetKey(KeyCode.DownArrow))
                 {
                     _bodyTranslation -= playerBody.up * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
                 if (Input.GetKey(KeyCode.UpArrow))
                 {
                     _bodyTranslation += playerBody.up * Time.deltaTime;
                     _bodyTranslationChange = true;
                 }
 
             }
         }
 
         // Rotations
         if (_bodyRotationChange)
         {
             playerBody.localRotation *= Quaternion.Euler(_bodyRotation);
         }
         _bodyRotationChange = false;
         _bodyRotation = Vector3.zero;
         if (_cameraRotationChange)
         {
             _playerCamera.localRotation *= Quaternion.Euler(_cameraRotation);
         }
         _cameraRotationChange = false;
         _cameraRotation = Vector3.zero;
 
         if (Input.GetKeyDown(KeyCode.Escape))
         {
             Application.Quit();
         }
 
     }
 
     private void FixedUpdate()
     {
 
         if (_bodyTranslationChange)
         {
             _rigidbody.AddForce(_bodyTranslation * Utilities.controls.playerSpeed, ForceMode.VelocityChange);
         }
 
         if (_jump)
         {
             _jump = false;
             _rigidbody.AddForce(playerBody.up * 500, ForceMode.Impulse);
         }
 
         _rigidbody.drag = playerBody.position.y > -0.6f ? 1 : 8;
 
         _bodyTranslationChange = false;
         _bodyTranslation = Vector3.zero;
     }    
 }

The main two problems are :

1. As I do rotations in Update, and movements in FixedUpdates, there is some annoying jitter when I both move and rotate at the same time. I tried to show this in a gif but everything seems laggy so I can't really show it.

2. As I use AddForce() to move my character, I had to increase the drag of my rigidbody (up to 8) si it doesn't "slide" when you stop moving. This works great but now I can't jump properly because of that. I found a workaround, by putting the drag back to 1 when I'm in the air, but then if I jump and move, I move 8x faster in the air which is annoying aswell.

Am I doing thinks completely wrong ? I first did not use AddForce but normal vector translations to move the character, but collisions were buggy as hell, I could go through most walls, objects... etc

Thanks if you read all that !