only just joined this forum so you might not be looking for answers anymore but:
My daughter has fibro and what has really really helped in strenghtening her muscles, toning her muscles and in general helping fibro flare ups reduce (basically getting out of the downward spiral she was in) is Pilates. One-on-one coaching was necessary and was very expensive but so worth the investment. Maybe where you live Pilates is cheaper but i would highly recommend it especially if you can get one on one coaching or at least talk to the trainer about your condition first ....
hope that helps... fibro s*cks and is very misunderstood