Player Controls For Restricted Directional Movement, but those things vary...

So I am making a little game.

My camera is working pretty well now thanks to @Bunny83.

And having applied that same camera rotation code to my Playerobject, the player now continues moving in the same on-screen-direction even though the game-space has rotated by 90° in whichever direction.

Now, however, I am back to the problem of player control input.

I want the player to be able to use WSAD or similar 4-directional controls to move the player-object in the corresponding direction. Problem is that in worldspace, the true directions are reorienting all the time because the player-cam rotates around the play space.

I have tried using self-space rotation on the player object, tried various Vector.3 things.

I really don't want to have to end up using just two keys for Turn-90°-Left/Right, because that become difficult to interpret when the playerObject is not moving in a scree-vertical vector from bottom to top of the screen.

Any ideas, Oh Great Internets?

playerObject Code:

     public float currentSpeed;
 
     public float curRotX = 0f;
     public float curRotY = 90f;
     public float curRotZ = 0f;
 
     // Use this for initialization
     void Start ()
     {
 
     }
 
     // Update is called once per frame
     void Update ()
     {
         curRotX = gameObject.transform.rotation.x;
         curRotY = gameObject.transform.rotation.y;
         curRotZ = gameObject.transform.rotation.z;
 
         ForwardMotion ();
 
         RotatePlayer ();
         RotatePlane();
     }
 
     // to cause constant motion.
     void ForwardMotion ()
     {         
         transform.Translate (Vector3.forward * currentSpeed * Time.deltaTime, Space.Self);
     }
 
 
     // to rate the player gameObject
     void RotatePlayer ()
     {
         if (!(Input.GetKey (KeyCode.RightShift))) 
         {
             if (Input.GetKeyDown(KeyCode.W))
             {
                 transform.Rotate (curRotX, curRotY, curRotZ, Space.Self);
                 Debug.Log ("Player Turned North");
             }
             else if (Input.GetKeyDown(KeyCode.S))
             {
                 transform.Rotate (curRotX, curRotY + 180, curRotZ, Space.Self);
                 Debug.Log ("Player Turned South");
             }
             else if (Input.GetKeyDown(KeyCode.D))
             {
                 transform.Rotate (curRotX, curRotY + 90, curRotZ, Space.Self);
                 Debug.Log ("Player Turned East");
             }
             else if (Input.GetKeyDown(KeyCode.A))
             {
                 transform.Rotate (curRotX, curRotY -90, curRotZ, Space.Self);
                 Debug.Log ("Player Turned West");
             }
         }
     }
 
     // to rotate the plane of play
     void RotatePlane()
     {
         if (Input.GetKey(KeyCode.RightShift))
         {
             if (Input.GetKeyDown(KeyCode.W))
             {
                 gameObject.transform.Rotate(0f, 0f, 90f);
             }
             else if (Input.GetKeyDown(KeyCode.S))
             {
                 gameObject.transform.Rotate(0f, 0f, -90f);
             }
             else if (Input.GetKeyDown(KeyCode.D))
             {
                 gameObject.transform.Rotate(90f, 0f, 0f);
             }
             else if (Input.GetKeyDown(KeyCode.A))
             {
                 gameObject.transform.Rotate (-90f, 0f, 0f);
             }
             
         }
     }
 }

I have a screen capture video but UnityAnswers hates me and wont let me upload a 1.17MB MP4.

On the start plane it works just fine, I can WSAD my way to anywhere I want to go.

However, once I start rotating around the play-space, and thereby changing my plane-of-play, the controls become less useful, until I have to try to guesstimate how to use them and resort to just using my A & S keys, which are still often inverted due to my orientation.