Add slippery player movement to button controls?

Hi, I have a game where my character moves, when i added the keyboard controls i made it so that the movement felt slippery. I now added buttons on screen for mobile although since i have added the PointerUp/Down script the movement isn't slippery anymore. I realised this is because that uses a bool to see whether the button is being pressed and when the button isn't pressed the movement is false and doesn't move a little further after pressing the button.

I really couldn't think of a way to do this and I was wondering if anybody else would have an idea. Thanks in advance and here is the code.

 void Update () {
 
         //Slippery movement with keyboard controls.
         float z = Input.GetAxis ("Vertical") * Time.deltaTime * moveSpeed;
         transform.Translate (0, 0, z);
 
 
 
 
         //Using the buttons to move.
         if (isUpPressed) {
             print ("PRESSED");
             transform.Translate (0, 0, (Time.deltaTime*moveSpeed));
         }
 
         if (isDownPressed) {
             transform.Translate (0, 0, -(Time.deltaTime*moveSpeed));
         }
             
     }
 
 
     public void onPointerDownUpButton(){
         isUpPressed = true;
     }
 
     public void onPointerUpUpButton(){
         isUpPressed = false;
     }
 
     public void onPointerDownDownButton(){
         isDownPressed = true;
     }
 
     public void onPointerUpDownButton(){
         isDownPressed = false;
     }