Secret : exclusive design rights for me total confidentiality

It is an invention. I have no pictures of it but it is fairly simple. Reminiscent of existing simple everyday consumer products. The design will just incorporate my straightforward modifications. The description of what is required will be easy to follow. I need a visual 3 D design to be made plus a version in a CAD format I could take away and deliver for production of more than one. Ideally however you would provide one 3D printed example, probably using plastic, so i could try it out in real life.I realise this might mean a separate charge for materials. I would need written confirmation in advance of the points in the project title. Justin North