First I bought a really cute little pink and black adjustable office chair from Office Max...for $29.00. It fit at my sewing table, was really comfortable and I loved it. But, you get what you pay for....it lasted about 15 months and then the hydraulic lift in it wore out (I may be plump, but I really don't think it was my weight that did it)
So, now I have a more expensive (and boring) black, adjustable office chair and it seems to be going to hold up. It really is important to have a good, adjustable chair, so you can change positions periodically.