In the coming months, I would like to start adding some exercise to my routine (on the theory that some aerobic exercise, strength training and flexibility will probably be good for my overall health, including brain health). Since my injury, I've limited myself to light household chores, some stairs, and fairly slow walks outdoors (20 mins or so).

Some possibilities include yoga, swimming, and stationary cycling (I love running, skiing, squash, and other activities, but those will have to wait). I'm actually thinking about buying a stationary cycle, as it would be something I could do readily from home. Yoga has some appeal as well, but I'm reluctant to do a lot of bending-over or upside-down poses, at least to start. As for swimming, I love being in the water, but I will need to get better before I start making treks to the gym.

Does anyone have any suggestions re (1) which exercise might be a good initial choice, and (2) how to build up tolerance gradually without triggering symptoms?

I'm thinking that having at least one rest day between exercise sessions probably makes sense to start (to see how I respond). And starting with very short time periods and exertion levels.