Hi Liz, I'm glad you're interested in ideas about exercise.  It's critical to good health in so many ways.  If you heat up just walking, you may want to explore some hormone therapy.  Have you had your thyroid checked?  had your yearly physical exam? If you're healthy and just get hot, don't be discouraged.  There are still exercises to choose from that don't have to be overly strenuous and still be of benefit to you. Yoga is excellent.  Yes, Pilates is hard, but don't expect too much of yourself at the beginning.  Keep at it and you'll be surprised how much strength and flexibility you will gain.  I'm not sure there's a better exercise than either Yoga or Pilates for overall body conditioning.  Tai Chi might suit.  Water aerobics might be just the ticket...a good workout in a cooling environment.  Good luck and keep at it,  Sandy