I have used two layers of batting on only one large quilt and it was DH's favorite quilt of all times. For me it was way to warm to sleep under and even more difficult to quilt. Even though that quilt has long ago worn out I still have to keep it for DH. He ask for it every once in a while. I have also use a double bat on a few baby quilts that I knew would be used for outdoor stroller use or to crawl on the floor usage. I always thought they would be to warm for crib usage.
Keep in mind twice the batting twice the warmth. Most quilts are warm enough with a single layer of batting and are much easier to quilt.