The house was built in 1905

I live in canada and it's getting pretty cold. The house my parents bought is a hundred years old. It's so old, it doesn't have asbestos It has horse hair plaster and it's not redone at all. There is no new insulation in the ceiling only the pine wood chips, and there's no insulated siding. that being said the walls are so cold and the upstairs bedrooms have no heat and the only access to heat is by leaving the doors open cause there is no vents, and as an adult with younger siblings and still living at home, I am not leaving my door open. That being said, I have plastic my windows, completely blacked out one window with garbage bags and insulation because it was damaged and I do have a space heater but the walls are still so cold and the walls themselves give off a draft. I also have reptiles, and i'm worried it might get too cold in my room for them Is there anything I can do to try and reduce the amount of heat, I'm losing.