Hobbs Heirloom wool or Quilters Dream wool would both be very warm and light. Wool is more expensive than cotton, though, and has its own problems -- especially potential bearding through dark fabrics.
I have lived most of my life in Minnesota and Wisconsin. We are used to layering. I would rather layer a blanket underneath a quilt than try to sleep under a quilt that is very heavy. Some people like really heavy quilts, but I think most people are like me and prefer medium weight quilts.