Warm n Natural has too stiff a drape for me because it is a batting that is needlepunched through a scrim. This makes it difficult for me to hand quilt.
I would think Hobbs 80/20 batting ((80% cotton/20% poly) would be a good choice, but check with your longarmer before deciding.
I once machine quilted a little doll's quilt with stippling. Came out pretty stiff! The amount of quilting you do in a space makes a big difference. Thread size also matters. You can quilt more closely with finer threads and not have the stiffness problem.