I really enjoy coconut oil as a rough weather gauge.
I cook with it a lot, but prefer it to be in liquid form for easy measure (which only happens in the warmer bits of summer here), so in winter, I keep a jar of it on top of a particularly warm heat vent.
I keep my place at 60f/15.6c in winter or it costs a fortune to heat. When it’s relatively warm out, the heat doesn’t kick on often enough to melt it, but when it’s real cold/windy the entire thing will be liquid.
Heated mattress pads on my bed and couch, mostly. And a heated chair pad when working. They cost a ton less to run than filling a drafty space with gas-warmed air, and are mostly sufficient. A month of both of the big pads being constantly on, on high, barely touches my electric bill, but my gas bill for heat… I keep it that cold because that’s still around $200 usd/mth. If I bump it to 65/18.3, it shoots up to the $350-400+ range. And since I’m not actually comfortable at 18.3 either (26-33/80-90 is about my sweet spot), might as well just keep it at 15.6 and save the money :)
So those, and fuzzy socks, fuzzy pajama pants, and a fuzzy bathrobe. Maybe a high-heat pad here and there, if I’m feeling luxurious or my back hurts. A friend of mine does something similar, but uses heated vest and socks to take the warm along with (rechargeable ofc).