I would not double up Warm n White. Especially if it's a large quilt, it will be plenty heavy with just one layer of batting. A few people will like the weight of a queen-sized quilt with two layers of WnW, but probably not most. I would not be able to sleep under something that heavy. Plus, it makes making the bed more difficult (all that weight!) and may require taking the quilt to a laundromat for washing and drying (if it becomes too big and heavy for a home machine). It will also make muscling the quilt through your domestic machine much harder -- more weight to have to keep evenly distributed, and the extra bulk will make the quilt harder to fit under the arm of the machine.
I vote for changing the batting, but only to a single layer of WnW!
I should probably add that I quit using Warm n Natural quite a few years ago. Although it has many great qualities, the needlepunching through scrim makes it more stiff than other battings. I prefer a softer drape in my quilts.