Parents got me one like this for a birthday pressie -

It's pretty great for watching films because it tilts back really far. I spend most of my time using my laptop in bed rather than sat in a chair though.
I also have one of these kneeling chairs

which are really good for your back - it distributes your weight between your arse and your knees and lets your back form a more natural shape. This is what i use for a long work or gaming session.