You might want to check out SparkPeople's Limited Mobility Lifestyle Center, since all of the exercises here can be done from a seated position: www.sparkpeople.com/resource/limited-mobil
Would swimming also be an option for you?
Are you currently doing any strength training? I would recommend asking your doctor for a referral to see a physical therapist who can create a program to help you regain strength on your left side and address your balance issues.
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everybody on the couch."