I keep my heat set to 60f/15.55c and use heated mattress pads on my bed and couch to make it tolerable. It has been between -7f/-21.7c and 24f/-4.4c this week, and it gets colder, usually mid January.

The cost to increase my heat from those temps to a somewhat more comfortable temp is literally hundreds of us dollars per month in gas, where the heated pads running 24/7 increase my electric bill by only a dollar or two a month (hydroelectric in my case, so hands down better, price difference aside).

The difference in operating costs is insane.

Heated blankets are a bit of a different thing; iirc they get warmer because they are meant to be above you, but could work the same way with that properly taken into consideration. You don’t get the sudden warm most of the time when using them under you, but it does help keep your core temp up. So lovely!