I usually put two chairs stacked for height. I was taught to sit without my back touching a chair back when sewing. In fact my grandmother's sewing chair was a three legged stool. Back held straight, no jutting forward or hunched shoulders. This was the way our Home Ec teacher taught us to sit when sewing. We could bend our heads down but never stick our necks out. In fact all my teachers insisted on good posture when sitting at our desks at school. And no slumping or slouching ever. LOL Prim and proper for sure but I have never had a back ache from sewing all day or sitting at a desk. Having good posture over the years is very important as we age.