Several things come to mind that might help you.. First, do add the backpack weight. I learned that on a trip I took with my granddaughter..It helps keep your shoulders from tensing up. Second, raise your sewing machine to a more comfortable height. I used Margarita McManus' tutorial for that, and it has made a tremendous difference. Third, adjust your chair height so that your feet reach the floor, but you don't have to bend or lean over your machine. And four, I recommend having your iron set up on a table next to you, so you don't have to get up and down too much. Of course, you need to take frequent breaks, too.
Hope all this helps.. but do take care of your body. You come first, then the lovely quilts... Hugs!