Good ventilation makes insulation mostly moot...and there are many cons, rodent housing, chickens eating insulation, etc.
Heating a coop is usually not necessary unless you have temps well below zero 24/7 for more than a few days.
You might find some guidance here:
https://www.backyardchickens.com/articles/cold-weather-poultry-housing-and-care.72010/
Tho I don't often get into singles or below, I've found periodic electrolytes can really help:
https://www.backyardchickens.com/articles/aarts-extreme-weather-spiel.75893/