Ash,
I took a yoga flexibility class at Michigan State University and it was specifically for arthritics and fibros. Always take a pain med before class, even if it's just ibuprophen. Also be sure that the instructor knows you have fibro. If possible, sign up for a class that's specific to people with joint/mobility problems.
There's a short descript
ion of movements and how they are done on this website. Very simple stuff. No weird poses or pretzel bends.
Yoga Flexibility SeriesMakes me feel awesome when I remember to do it about
once a week.