Dan Savage wrote in his advice column once that if you can't find a 'mistress,' make one. It's great advice.
One thing to keep in mind is that, while it does depend a lot on how open minded your partner is, generally speaking your partner is going to want to give you pleasure and satisfy you.
Women aren't locked up in drawing rooms anymore. Most adult women are gong to be aware of the fetish world generally, and not just from tv and movies. Many may even have specific experience with it from their own relationships, if not second-hand experience from hearing about it from friends who've met kinky men. So even though it can be frightening and hard, your best bet is honesty. Tell your partner what turns you on, and usually she'll do it to/with you.