I set straight up, shoulders back, looking down at the machine needle. I don't lean in, just lower my head and never jut it out. My sewing machine throat plate is the height of my arms bent at the elbows. I took the back and arms off an office chair and only use the seat part. Like a rolling chair in the Dr. office. My grandmother used a three leg stool for her sewing chair and I learned to sit on that to sew. Her back, shoulders or neck never bothered her if she sewed all day. Proper posture while sitting is a must. I tend to sit on a sofa or chair without touching the back. I have to check myself when visiting, some take it as being too prim. But my back never hurts. LOL.