Don't expect doctors to necessarily have your quality of life foremost in their minds. When they say "it would be easiest to do X", ask them whether it's easiest for you the patient or them the doctor. Similarly, "it would be best"
Find a cancer support group and talk to them. Find your local branch of the Cancer Society and talk to them. These folks can give you emotional perspectives that you can't get from doctors. (e.g., "What's it like to have only one breast?").
Double-check every medication you're given to see whether it interacts with your others. One of my relatives is constantly catching doctors attempting to prescribe dangerous cocktails. "Oh yeah, you're right. Try this one instead," they'll say.
Read up on side-effects from medication and be vigilant. Again, relative kicked cancer without blinking, but the complications of treatment nearly killed her, and drugs damaged her liver, gave her a heart attack, and brought on diabetes.