My mother has back problems...
She has a Scholl Massage/Heat pad, and finds it very helpful... It has a vibrating massage function, and a heat facility... You can fit it easily with it's velcro straps to any chair... And it has an attatchment that you can plug into the lighter facility of a car, so you can use it on the move, too...
We bought this in Boots, I think, and it was about €80... Well worth it for the relief it gives Mum...