you might think I am crazy, but I'd go with a wool bat - incredible breathability - warm in winter and cool in summer. plus you can't beat the stitch definition you get with wool. I, too, live in Texas and use wool in all of my personal quilts. my internal temperature also runs very hot, but the wool works for me,
if you go with a cotton, you could always use a thinner loft, like quilter's dream (They have multiple lofts of cotton) or even use plain old muslin inside your quilt to give it some body, but not a lot of weight.