Warm n Natural is a cotton batting, but it's needlepunched through scrim. The scrim makes it somewhat more difficult to hand needle than a cotton batting without scrim.
My favorite cotton batting, Mountain Mist Blue Ribbon 100% cotton, is hard to needle also but for different reasons -- uneveness, oils in the batting, etc.
One of the better battings for hand quilting is Hobbs 80/20 (80% cotton 20% polyester). A lot of hand quilters also like Quilter's Dream (a flatter batting than Hobbs, I think).