The trick is to make sure that everything is the right height, I think. You should be able to put your feet flat on the floor so that your thighs are at right angles to floor. The desk needs to be the right height too so you are bent too far forward . I agree that an office chair would be fine so long as it is adjustable so that you can get your body properly aligned.
This is explains it better than me. I think the only thing you can do really is try out some chairs. Go to Staples or Ikea or something and see what they have that suits you.
I used to have an office chair when I did it for a living - comfortable enough to sit back and hand finish. Now I don't do so much I have a stool and sew at my cutting table, which I actually find more comfortable/easier now.
I basically sew for a living now, im in the process of setting up my own business so need a decent chair that wont kill me whilst i sew my fingers to the bone.
At the moment i have a cheapy chair from ikea, and oh my god today after sewing non stop for past few weeks i feel as if ive run a marathon, im aching all over, My back hurts when i move and I can only assume its the chair ove been using.
Any ideas for a reasonable priced one, under £100 at least.
The horn hobby chair is my fave but way out of my price league right now, thanks