I have a similar issue, after an hour at a machine my back is screaming. I've tried every type of set up for the machine, but nothing helps. I can sit on the couch or in a comfy chair and hand sew for hours. Currently working with hexagons is my favorite. I did a slightly modified GFG in a queen size and a crib size GFG with small hexis for my granddaughter. Newest project I am trying to give a modern or manly twist to so I am using just three colors, red batik center, dark blue batik around the center to make a diamond shape and then a gray path.
But honestly, most any pattern you like you can hand piece. I use 1/4 inch quilting tape to mark my seam width when I am piecing squares and triangles.