I make seasonal soap for a lovely “you pick” farm in Gibsonville, North Carolina, called Blueberry Thrill Farm. Using their herbs and flowers I create soap for them to sell at a little house they have on site. In the past I have made blueberry soap along with lavender and herb soaps, always with their product.
If you are looking for a niche, consider finding something local or consider a place you have visited and love that you could be a part of with your soap. I have three places now that sell my soap. Two because I found a use for products they use and one because I love the area and store and visit often.
Consider your area. Are you near a farm? Can you make a good soap using their flowers or herbs? What about using goat milk or making a felted soap with lamb roving? Do you have a favorite craft brewery near by?
For example, I asked for some leftover mash from a distillery. It was a disposable product to the company and to me it was a good additive for soap. I promised that if I could come up with a good soap I would share it with them. I did, they loved it and it became a unique promotional product for their company.
Remember that while it is all about your love of soap making, it is not all about you. How can what you do enhance their company? How would your soap fit there? What would make it attractive to them? These are all things to think about if you want to go this route.
Make a good soap and make a good local connection. And have fun!