Indeed, you should not limit yourself to just one company, since there are many professionals in the world who can realize your idea. I can also recommend one of these IT companies, which also deals with saas product development. It is called CodeIT and you can read in more detail about their services on their website
https://codeit.us/services/saas-development . I think you may well like them, as they have a strong business analytics department, where professionals will help you define and clearly describe product requirements, and can also give real advice on how to implement your business requirements.