Back problem, exercise and weight loss.

Hi, I'm in my early fifties and last year suffered a herniated disc in my lower back. This has caused permanent nerve damage and the sciatic nerve is trapped. Intensive physiotherapy and wearing a lumber support when working has helped, and if I'm careful I don't suffer any pain. I've struggled to keep my weight down over the past twelve months, but now am doing well using the mfp. I've lost over 3 kg so far. I walk at 6 - 6.5 on a treadmill everyday, do 10 or 20 minutes of body weight exercises, following a DVD, and a little yoga. I would like to do more exercises, but worry about aggravating the injury. Swimming was recommended too, and I'll be doing that when it's warmer. Any other suggestions?