My gf is a yoga instructor and I go to her class almost every Sunday morning. She has students with weight problems. A good instructor will always have ways you can modify a pose to work around size and injury issues. I say give it a go. Start with an easy hatha class or similar, talk to the instructor, and go from there.
I personally have balance issues related to the after effects of a severe TBI and find the yoga useful for improving my balance and as a cross training strength/weight bearing exercise session. There is also a mental/meditative benefit similar to a good road ride.