you really need to avoid those general niches, like pornstars (young or old) or any standard fucking, imo.
you either have to go in an extreme niche, like pissing,squirting,gag,bdsm,etcc.. or kinda
or you can go in more soft niche, like teasing, voyeurism, etc..
here's one of my favorite sponsor with niche sites that are really converting :
Serious partners 
good luck in your new ventures