Double jump feels really off

Hi there

Pretty new to Unity. I'm messing around, trying to make a simple 2D platformer.

I managed to implement basic movement and jumping. My next challenge was to create a double jump. It "works" but feels really off. Basically what happens is that the later I press the jump button again, the less I actually jump. So as I'm falling down, I barely get propelled up anymore, if at all. So basically, double jumping only really has an effect at the beginning of a jump. And even then, the result varies. I want the effect of the jump to be constant and not to be dependant on my current jump arch.

Here's the code that is relevant to moving and jumping. Note: A lot of the code stems from this video right here.

     int count = 0;
     public Text countText;
     public Text winText;
 
 
     float maxSpeed = 10f;
     public float jumpForce = 70f;
 
     bool isFacingRight = true;
     private Rigidbody2D rb;
 
     bool grounded = false;
     public bool doubleJump = false;
     public Transform groundCheck;
     float groundRadius = 0.2f;
     public LayerMask whatIsGround;
     Animator anim;
 
     // Use this for initialization
     void Start ()
     {
         rb = GetComponent<Rigidbody2D>();
         anim = GetComponent<Animator>();
         winText.text = "";
     }
     
     // Update is called once per frame
     void Update ()
     {
         if ((grounded || !doubleJump) && Input.GetButtonDown("Jump"))
         {
             anim.SetBool("grounded", false);
             rb.velocity.Set(rb.velocity.x, 0);
             
             rb.AddForce(new Vector2(0, jumpForce));
 
             if (!doubleJump && !grounded) doubleJump = true;
         }
 
     }
 
     void FixedUpdate()
     {
         grounded = Physics2D.OverlapCircle(groundCheck.position, groundRadius, whatIsGround);
         anim.SetBool("grounded", grounded);
         if (grounded) doubleJump = false;
 
         float move = Input.GetAxis("Horizontal");
         anim.SetFloat("Speed", Mathf.Abs(move));
         rb.velocity = new Vector2(move * maxSpeed, rb.velocity.y);
 
         if ((move > 0 && !isFacingRight) || move < 0 && isFacingRight) Flip();
     }

Is there any way I can improve my double jump so that it feels more like in other games and isn't affected by how fast down I'm currently going? (i thought rb.velocity.Set(rb.velocity.x, 0); would fis this but apparently not..)