Which chair is good for my back?

Office Supply store. Go to an office supply store and try sitting in several of them to see how they feel to you. Since everyone is different you need to find the chair that fits you best. If you spend most of your time in this chair don't scrimp on it; it is an investment as important as the right car. You want good support for the back with your feet flat on the floor and no pressure on the back of the legs.