I do this a lot. I am also in the deep south and we rarely need heavy blankets. Flannel backing with no batting makes a nice lightweight quilt that is soft and drapes well. I made one for DH this way and he uses it as a throw on the sofa all the time. Use a good quality flannel, and like the others said, definitely prewash. I am not a dedicated prewasher, but I ALWAYS prewash flannel, often two or three times.