Getting Sprite height/width in local space

I'm playing about in Unity2D trying to move two separate objects with the analog sticks.

When they go out of bounds of the camera - I want them to stop.

The sprites have a rigidbody2D attached (I found characterController had collisions between the two objects which I didn't want).

While I can get the objects to stop at the edge of the screen, half the sprite goes out of view as the position is measured from the centre of the sprite.

I'm having trouble preventing this however as the sprite width/height seems significantly larger than what's displayed on screen.

How should I be getting the actual size of the sprite?

Code below:

// Use this for initialization void Start () { rigidBody = GetComponent (); spriteRenderer = GetComponent ();

     halfWidth = spriteRenderer.sprite.rect.width/2;
     halfHeight = spriteRenderer.sprite.rect.height/2;
   
     //Get the bottom left as a world co-ord.
     screenBottomLeftInWorld = Camera.main.ScreenToWorldPoint(new Vector2(0,0));
     //Get the top right as a world co-ord.
     screenTopRightInWorld = Camera.main.ScreenToWorldPoint(new Vector2(Screen.width, Screen.height));

     Debug.Log("bottomLeft " + screenBottomLeftInWorld.x + " , " + screenBottomLeftInWorld.y + "topRight " + screenTopRightInWorld.x + " , " + screenTopRightInWorld.y);
 }

 private float halfWidth;
 private float halfHeight;
 
 private Vector2 screenBottomLeftInWorld;
 private Vector2 screenTopRightInWorld;

 private SpriteRenderer spriteRenderer;
 private Rigidbody2D rigidBody;

 // Update is called once per frame
 void Update ()
 {
     float xDirectionShipTwo = 0;
     float yDirectionShipTwo = 0;

     if(Input.GetButton("ShieldTwo"))
     {
         Debug.Log("Shield two active");
     }

     if(Input.GetAxisRaw("ShipTwoHorizontal") < 0)
     {
         xDirectionShipTwo -= speed;
     }
     if(Input.GetAxisRaw("ShipTwoHorizontal") > 0)
     {
         xDirectionShipTwo += speed;
     }
     if(Input.GetAxisRaw("ShipTwoVertical") > 0)
     {
         yDirectionShipTwo += speed; 
     }
     if(Input.GetAxisRaw("ShipTwoVertical") < 0)            
     {
         yDirectionShipTwo -= speed;
     }
     if(Input.GetAxisRaw("Fire2") > 0)
     {
         Debug.Log("Fire two hit");
     }           

     float proposedX =  rigidBody.position.x + xDirectionShipTwo;
     float proposedY = rigidBody.position.y + yDirectionShipTwo;       

     if(proposedX < screenBottomLeftInWorld.x)
     {
         proposedX = screenBottomLeftInWorld.x + halfWidth;
         Debug.Log("New x " + proposedX);
     }
     else if(proposedX > screenTopRightInWorld.x)
     {
         proposedX = screenTopRightInWorld.x - halfWidth;
         Debug.Log("New x " + proposedX) ;
     }

     if(proposedY < screenBottomLeftInWorld.y)
     {
         proposedY = screenBottomLeftInWorld.y + halfHeight;
         Debug.Log("New y " + proposedY);
     }
     else if(proposedY > screenTopRightInWorld.y)
     {
         proposedY = screenTopRightInWorld.y - halfHeight;
         Debug.Log("New y " + proposedY);
     }           

     Debug.Log(proposedX + ", " + proposedY);
     rigidBody.MovePosition(new Vector2(proposedX, proposedY));
 }