I went to an ergonomic talk at the Maine Quilt show. The speaker said to keep your ears over your shoulders - you can even slouch that way and be ergonomically correct. She also said to use a recliner for handwork. You want to keep yourself from hunching over/leaning over your work and bring it up closer to you to prevent this. Oh, and drink lots of water so you have to get up and take a break now and then.
Hope this helps.