Sexy is a state of mind. Yes, what you choose to wear to your boudoir session obviously adds to that, but really, don't over think this!
Go with what feels like YOU. What YOU feel best in. These sessions are an intimate experience, and the last thing you want to do is feel totally unnatural with what you're wearing.
A lot of women have been wearing body suits lately because they're inexpensive AND comfortable. They can be simple like my girl Kat's (pictured below) or you can go lacey and super revealing.
Check out my babe Kat, and how she rocked the hellllll out of a simple, inexpensive, white body suit!