I'm not sure if what you have in mind is to use to layers of batting that you already have but, if not, I would suggest using Quilters Dream cotton batting. That is my very favorite batting and it comes in different "lofts". I recently used the Deluxe High Loft for DGD's quilt. That batting combined with flannel backing makes one heavy quilt! I do free motion quilting on my domestic sewing machine and that gave me a run for my money! It felt very warm to me while I was hand sewing on the binding, of course it is summer time. I'm getting ready to mail it to her and my DH said today he would like to keep it to use through the winter
He thought she would appreciate more when she's older. Ha Ha. Anyway, Quilters Dream is available at many LQS and online. This particular one I ordered through Amazon. Good luck on your search.