I've done yoga - I do yoga. Daily. It's been fabulous for spasticity and balance. I'm a full-time cane user now but was able to hold it off for years through a combo of balance PT and, IMO, yoga.
My suggestions:
1. Try to find a yoga teacher who has worked with people with MS. I've met yoga teachers who didn't have that experience who thought MS issues were muscle issues. And, they might be but they're message issues first.
2. Make sure the practice studio is cool or will provide a fan. Because of the popularity of "hot yoga" and the prevailing theory about warmth is good for muscles, many yoga studios are too hot for us.
3. If your balance is bad, don't dismiss chair yoga. It's great. You can also use lots of different props which a teacher who understands MS will hel you with.
I'm a firm believer in the "use it or lose it" and "exercise is important" schools of thought. I've had MS for at least 20 years and have seen big differences in my ability to move depending on if I'm exercising or not. Have fun!
I have done yoga. I found it was great for spasticity. I even did chair yoga taught by a woman with MS with movements geared to MS patients.
Alex