Wool batting is the warmest. I would use Hobbs wool.
You can layer battings. I would layer Hobbs PolyDown on top of wool for max warmth. It is probably not advisable to layer battings if you are hand quilting; layering battings is down primarily when machine quilting.
Warm and Natural is not made by Hobbs; it is made by the Warm Company. This is a dense cotton batting that is needlepunched through scrim. It is thick and heavy for a cotton batting, and very stable, but not necessarily any warmer than some polyester battings that are much lighter in weight (such as Hobbs PolyDown). W&N is used a lot because it can be quilted up to 10" apart. W&N is one of my least favorite battings because of its weight and stiffness (although it does soften up a little with each washing).