Heya Andre,
I've pushed quite a bit of NN content over the years and there are a few out there that sell well, which I'll name at the end of this.
The problem with NN is that it rarely retains and is usually priced less than nude sites, so your $ is lower both for the join and retention.
If you decide to dip into NN, i suggest you keep an eye on the sites that have webcam shows. Those will be your best bet.
Here are some NN sites I've had decent success with:
www.pattycakeonline.com
www.lilijensen.com
www.truetere.com
www.nextdoornikki.com (even though she's only got a piece of dental floss covering part of her nipple, somehow thats considered NN
)
www.karisweet.com
I typed these in off the top of my head, so if there is a typo, i apologize in advance.
Those are the ones off the top of my head. the first two I noted are probably my best converting for NN.
good luck with the niche.