I've never put much thought into this but my mother who spent some of her teenage years in the UK in the 70's used to use a hot water bottle. Here in the US, we had a mid-century ideal of "energy too cheap to meter" that would have been provided by the burgeoning nuclear industry. It never really panned out, but a lot of houses had things like radiant heaters in floors and room wrapping baseboard heaters installed for comfort which is nicer than having to deal with a fluid filled bladder, but obviously much more costly.