It's been 17 below in Wisconsin this past week, and below zero a lot since the middle of November.
After reading all these posts, it seems three things stand out to make quilts warmer:
Wool batts.
Tied, not machine quilted.
Layers of quilts, with wool nearest the sleeper.
I have a purchased comforter with a machine quilted quilt on top. That's warm enough most nights. But sometimes, I'm just freezing, which has nothing to do with the weather or the temperature. It's just me. (It's probably because I've been sitting around doing nothing for a few hours.) Then I layer on my heavy wool afghan. That does it.