Definitely thick curtains and "snakes" for all cracks is key. Plastic the windows. Seal up everything. My friend in Alaska lined all her walls with books to provide natural insulation. Rugs for the floor. Heavy blankets for the bed, throw blankets for the couch. Thick sweaters
When you look at English dramas they are often wearing 8 layers of clothes, to stay warm. That way you can add and remove layers as the room warms and cools.
Drink hot tea
I'm doing that now!
