I did mine about 2 months ago. You're right, sneezing is very unpleasant. For me it turned into subdued laughter. I'm all good now. You will be too, soon. It usually doesn't take too long for those ribs to heal. I did my right side wrestling a calf, and then did my left about six weeks later riding my bike - correction - crashing my son's bike. Exercising with broken ribs, I don't know. Like you said, walking would be good.
The riding is almost over here in northern Alberta, so you won't be missing much. Better broken now than 3 weeks ago.
Get well soon!