I had to give up on my Forever 21 leggings after a friend informed me that she could see my butt cheeks through them at yoga. The American Apparel winter leggings for $38 are my savior.
I got my AA leggings because of a rec from /u/krebhamp on this leggings thread.
Here is another awesome leggings thread: Best brands for quality leggings or just any result from searching black leggings.
NOTE:
I'm 5'4 with short legs, so the inseam is a bit long on me. Otherwise a small is a perfect fit. I'm normally a 4 but have narrow hips/flat butt. I'm thinking a medium would be a good fit on you. My big-bootied friends have vouched for the AA thigh-rubbing quality.