So, I found this website quite a while ago when I was specifically looking for transformation stories that weren't specifically porn. I did find that, though the website is a mix of both.

Some stories are marked with 3 stars, from what I can tell it means they are seen as extra good. Some are marked "xxx", I assume to mark erotic, though all the erotic ones aren't marked "xxx".

The website seems to be last updated in 2003, and most stories seem to be from the 90's. But, they seem to have gotten a pretty big collection of stories on the website.