Rotate sphere to the direction of movement

Image a 3D rigidbody ball with the blue square on top. This is my character (see picture 1.). Below is the script I use for moving the ball.

 void FixedUpdate()
     {
         if (Input.GetKey(KeyCode.W))
             rb.AddForce(Vector3.forward);
         if (Input.GetKey(KeyCode.S))
             rb.AddForce(Vector3.back);
         if (Input.GetKey(KeyCode.D))
             rb.AddForce(Vector3.right);
         if (Input.GetKey(KeyCode.A))
             rb.AddForce(Vector3.left);
     }

Now, I move forward and the ball rolls forward (see picture 2.). The top of the ball (blue square) is now facing the front. Here comes the tricky part for me. When I move left/right I want the ball to rotate first and then move (see Picture 3. <-- link). In other words, I want the blue square to be always facing the direction of movement, therefore getting in contact with the floor every full roll. What previously (from the ball perspective) was right direction, should now be forward again. I would appreciate any sort of help. Thank you in advance.