2D Player Movement C#

I have a script for basic movement that works, but I want to be able to steer the players horizontal movement while midair. I also would like to be able to determine the force or the height of the jump by how long I hold the jump button.

Here's my working movement script so far:

 using UnityEngine;
 using System.Collections;
 
 public class Player_movement : MonoBehaviour
 {
     public float f_speed;
     public float f_jumpSpeed;
     public float f_gravity;
     private Vector3 v3_moveDirection = Vector3.zero;
     private CharacterController controller;
     
     void Awake ()
     {
         controller = GetComponent<CharacterController>();
     }
     
     void Update ()
     {
         if (controller.isGrounded)
         {    
             v3_moveDirection = new Vector3(Input.GetAxis("Horizontal"), 0, 0);
             v3_moveDirection *= f_speed;
             
             if (Input.GetButton("Jump"))
             {
                 v3_moveDirection.y = f_jumpSpeed;
             }
         }
 
         v3_moveDirection.y -= f_gravity * Time.deltaTime;
         controller.Move(v3_moveDirection * Time.deltaTime);
     }
     
 }