I keep our thermostat at 19C - I turn it up to 20C if it is really cold outside. Blip has a Snugglesafe overnight as I have the central heating turned off completely from 22.15 - 05.15 all year round.
21 is over 70F, Gill: it's very warm for a house.
As you say, Mark, cats have a much higher body temperature than we do: hence my assiduous use of the heat pad for Blip.