I don't know how much it would cost to replace those windows with a double hung window and stick a window AC unit in there. Certainly cheaper, I would think, than setting the entire house at 60*.
I have the same situation that you do, except I have double hung windows and I put a window unit in there for a few months of the year. But before I got that I would sew downstairs during the day when I could. Usually I just sewed at night and early in the morning.