Books to introduce more variety in my sex life?

I think I'm good in bed, girls tell me that often, but I feel like I'm going to start doing the same things over and over if I can't start to introduce more variety into my sex life. Looking for books to read about sex and even long term relationships. I got a good girl right now and I don't wanna fuck it up.

Thanks!

P.S. Also really interested in advanced slave/master relationships.