Hi there LaLa, I have been doing Tai Chi for five years and am now a team leader/instructor.
I was diagnosed with b/c in 2010 and had a r/side mastectomy and lymnph node removal. i resumed tai Chi two weeks after surgery .... sitting in a chair doing restricted movements. As each week passed I did what my body allowed and within two months was standing again, doing full movements. I still get tired and when the bones go into "go slow" mode (mainly thanks to the arthritis and side effects of the Arimidex) I rest.
If you google "Paul Lam" or go into You Tube and do a search you will find a range of DVDs. There are a lot of proponents of Tai Chi but these have been formulated by Dr Lam and target all parts of the body. The one we use is Tai Chi for Arthritis.
I guess with any exercise the main thing is to listen to your body ..... it will tell you when it has done enough, then it's time to rest.
Take care of yourself
Cheers ... Shirl x0x