If you like Degrees of Lewdity and BDCC, I recommend Lilith's Throne. It's like... Take CoC2 or TiTS, but make it freeform rather than pre-written scene-focused. No worrying about if what you're wanting to do was thought up by the developer and looking up how to achieve it - you just enter a sexual combat system where (depending on who is the dom and who is the sub) you can do whatever you like, however you like