Udayana
Do what I did a month or so ago - buy a Swiss ball. Mine cost about £27 and the chap in the sports shop pumped it up for me properly. I have been using it to sit at the computer and rarely use the chair now. Just by sitting on it you are automatically strengthening back and abdomen muscles. It works!!
My older son has been using one in the office where he works since a friend recommended it and he said I ought to get one, but of course I didn't! However, seeing the physio a month or so ago in order to ask if she had any extra exercises for left hip and back, she said she couldn't think of any more than those I am
doing, but then wondered whether a ball would be a good idea. She was concerned that my balance might not be good enough because of the lack of vision, but in fact it was fine. I thought the chairwas comfortable but now I hardly ever use it! My son said, well I won't say I told you so, but I told you so!!:)