OOoooo great idea. Love it, keep em coming! A 10F comfort (traditionally -5F En rating - lower limit) would be beautiful. It’s definitely on the radar especially if we sell these ones well!
I’ve also been toying around with a “booster sheet” concept, which would be a very lightly insulated sheet or blanket that can be added to any quilt and boost the temp range by 10 - 20 F (so our 30F would become a 10F with the booster). Or you can use the booster on it’s own between 50 - 70F