It is very important at the early stages of your design, to pin down and write up a clear Product Design Specification.
A good product specification, will save you development costs and time. Plus will ensure that your chosen supplier can meet or exceed your needs. I have written a template that explains some of the concepts, and also is useful to batten down ideas into a concrete plan.
You can download the instructions and Product Design Specification template here and use it right away!
Good luck in your aims, to get specifically what you want. At the price, timescale and quality you want.
Regards,
John Biddleston