I operate numerous businesses in niche fields and I know several Life Coaches and Self-Development coaches.

From what I see with all of these examples, firstly your customers will be buying into YOU so make sure you have a unique and relatable story and experience to draw on. For instance, one coach I know quit drinking alcohol to improve his health and relationships, and then started a "30 Day No Alcohol challenge" product. If you can draw from your own journey to create your niche, you will have more credibility.