I live in Nevada and like cool quilts as well. What I use for batting is Bird's Eye Diaper cloth, which is cheap and can be found at:
http://www.fabric.com/SearchResults2...3-26a376046a5ee
Sometimes I use fleece as the actual backing, and sometimes just quilting cloth. What the Diaper cloth does as batting is it allows the quilt to breathe, gives "body" to the quilt, and prevents your piecing from showing through on the top. I love it! I learned to do this when I lived in England, and trust me, everyone uses diaper cloth for everything over there!