It would be nice if you could create your own working prototype. Hopefully you can. I started my prototype with cardboard and paints. I cut it to the size I envisioned and painted the design on the pockets. I know it seems elementary but it enabled me to make changes before we began sewing. I had my mother sew the first bag which ended up being more difficult than we expected. This will give you an idea of the time that goes into a finished product.
Remember, you don’t have to worry about color choices and materials at this stage. You will get a better feel for this once you begin to see price quotes. The purpose is to have a working prototype that you can present to a manufacturer. They will give you options at this point. Remind them that you have a provisional patent (patent in process) and have them sign a non disclosure stating that they won’t reproduce the product. It’s just extra protection.
I wanted to keep the manufacturing in the US so this is where I began. It is easier to find manufacturers in your area and makes it convenient to make changes. If you decide to go oversees, at least you now have some experience.