right now, in my specific apartment? internet.
the lady who lives above me is 90 and keeps her thermostat set way high (and still walks around bundled up). my apartment is also right above the furnace.
I have the radiators turned shut in every room but the bathroom and a window open and that just barely makes it tolerable (I'm still only sleeping under 1 blanket, when ordinarily I'd love to be under 2-3)