Not sure what the difference between Hatha yoga and yoga is, but my gym offers a yoga class which I try to attend at least once a week. I love it! It's not only helped me with my flexibility but also to relax. It took me a few classes to get really into since a lot is also about breathing and focus. I wouldn't worry about your flexibility, we've had people in the class that are recoverying from back injuries, etc. The instructor tells us the positions then shows us how to modify based on your flexibility and level. She's always very specific about honoring your limits. We have all different levels in my class, from people who have been doing it for 5-6 years (they're impressive) to those that just walked in the door that day and can barely bend over.