[maddz]

The other thing I would recommend trying is sitting every so often on a gym ball; that will help with posture and core muscle exercise. You'll wobble around alarmingly at first and will have to kneel straddling the ball with your toes on the ground, but if you persevere you'll end up kneeling on the ball with your feet tucked up. (Not recommended if you have to wear a skirt at work!)

Alternatively, if your knees will take the pressure, try a kneeling stool (be warned, they can leave you feeling mildly skinned if the fabric is too harsh). Compared to a gym ball, they can be very expensive though.

I have various Callanetics DVDs, but it's best if you can find a class. Alternatively, try yoga - I did supple strength classes for a while which is very similar to Callanetics (some exercises I couldn't do because of back problems but on the whole I could cope). Pilates I found put too much strain on my back.