OK so, this is a little bit more of a sketch of an idea than a full-fledged one. I'd love to talk it over though. The idea is that your character, for reasons of his or her own, decides to purchase a sex bot (that won't be the term we use in the story), an android, built to be female in appearance. However, the android is able to swap out parts, fitting a penis and testicles instead, whenever wanted. Other kinks can be worked in as well.
Again, I know, this is kind of vague and I'm usually much more detailed in my story requests, but it's late and the idea isn't really complete yet.
If this at all sounds interesting, let me know in a PM.