That's a common fear, but you are better off putting that aside and just going for it. Instead of worrying about someone taking your idea, have any manufacturer, pattern maker, etc sign an NDA, and move forward with your idea. And most importantly, work with people you can trust. Even if your ide...
Sounds ambitious! What are the key challenges for you? Are you able to develop the product yourself, and just looking for ideas of how to grow it to millions of users? Or do you need to find people to build the product/app itself? There are lots of resources available for both.