I'm asking specifically for a bootstrappable niche market, no VC.

Assume that you have found a niche market that is growing, reachable, and right in the "sweet spot" of not being too small, and not being too large, and you know the market has money to pay.

Note that my question wants a "data-driven" answer, not just your gut-level hunches. By "data" I don't mean only statistical data, but input from the market.

List (in order) the steps you would take to discover what this market needs. If you can, be specific with it and justify your approach. Compare and contrast to other approaches and why you think yours is better would be helpful.