Mechanical engineering drawings for XBOX ELITE and XBOX one regular controllers

I want to hire a designer that will be creating an accessory that mounts on the xbox controller. The design will be similar to the photo attached. We are looking to improve on this design mechanically. CAD files for the XBOX controllers can be found online for the starting point. The product will have a plastic injection molded base with arms. We need to improve the cutouts for the button access on the controllers. All points where fingers make contact with the controller must be soft rubber. The metal arms connect to a snap system in the plastic and are easily replaced. They cam to make contact with the buttons the concept is to allow the user to keep their hands on the controller at all times and speed up control of the buttons on the front of the controller. The current competitors design is not easy to use and is prone to failures. Need to improve on the design. I need concept drawings in Solidworks and renders of the final concept as well. We can collaborate quickly on skype.