When my son was stationed in Yuma, AZ, I made his quilt with no batting. It was made with polished decorator cottons, so it was a little heavier than quilting cotton. I think flannel would be fine. Just be sure to preshrink it well. On the other hand, everything there is likely to be to have AC, so a thin batting wouldn't be too much. I don't know which ones can have less quilting.