who said you need only 1 niche?
you can choose as many as you can and preferably the ones that you understand and know what customers/audinces wants
so you find random products and search/pray you find demand for those products? That's not how it is supposed to work.
you'll end up wasting time and thinking and probably money too, and in the end you won't find demand
if you do it in reverse, you'll guarantee finding success
find a niche/niches and find out exactly what problems to be solved and gap to be filled, and then look for a solution for these niches and solve their problem by marketing to them what they need.