I do tai chi. The slow movements really help build muscle and help with balance, alignment and breathing. I would never be able to do weight training. I also get costochondritis at times and know how you feel!

Hi @hmccarth5, google Dr. Loren Fishman, 12 Poses vs Osteoporosis. There is also information about the study he is conducting at http://www.sciataca.org
Algaecal has 3 different videos of the 12 poses on YouTube - there is one for the regular yoga poses, one modified for osteopenia and one for osteoporosis. Maybe you'll be able to tolerate them. I did the one for osteoporosis for a couple weeks and am now doing the osteopenia one. Since the poses are isometric, you may be able to tolerate them.
Also, with the weight training, were you doing chest exercises that caused the costochondritis? Maybe the weights you were using were too heavy. Margaret Martin, Melioguide, has some very good weight training videos. You can subscribe to her by email and she will send links. Carol Michaels is good as well and has videos on You Tube. Both Martin and Michaels are physical therapists who specialize in osteoporosis. Don't get discouraged. There are exercises you can do, you just haqve to find what works for you.