Mountain Mist Blue Ribbon 100% cotton batting gets softer with every washing, so this is the one I use exclusively.
I used to use Warm 'n' Natural, but that is a batting that is needlepunched through scrim. This makes the drape of it stiffer.
More quilting makes a quilt stiffer, but also the type of thread makes a difference. Finer thread will not stiffen the quilt as much as regular weight thread. So Fine is an example of a finer weight quilting thread.