For more warmth?
Double layer of batting?
Or use two quilts/blankets/comforters?
I think I would go for using two "thinner" coverings instead of one really thick one.
When I was growing up (back when the dinosaurs still roamed the earth), "heavier" - as in weighing 8 pounds instead of 4 - seemed to mean "warmer."
However - those quilts were washed very very very seldomly. "Freshening" was about as "clean" as they got. They would be put on a clothesline - the dust beaten out of them - and if it was winter - some snow might have been brushed on and off them. Did not want them to get "soaked" - because that would have taken a looooong time to dry the quilt.