Designing a brand new product is actually more difficult to get right than you might think. You may be tempted to just try your hand at it yourself, and who knows, you may even be successful at it, but you should know that there is a a tried and tested science behind product design; a specific criteria upon which a product can be designed to meet the tastes and needs of the users of the products.
The people who design products for others are usually referred to as product design consultants. These individuals will typically have a university degree in design, of which a significant portion of a lot of the available courses is focussed upon product design. It incorporates the learning of various psychological stimulus with the artistic sense needed to carry it through in a unique and stylish way. The process will develop your product with an understanding of ergonomics and aesthetics engrained into the end-product.