@Brydo During the coldest months especially if we have freezing temperaturers the overnight internal room temperature can drop to around 13c to 15c, in which I set my thermostat to 11c. When switching the heating off at night I switch the thermostat to auto so it comes on an hour or two before I get up.
This time of year the thermostat rarely drops below 17c unless we have freezing temperatures overnight.
My house is in a very open location on amountain and is your typical 1960s house. Its by no means airtight as it would affect the fabric doing this. The loft however is insulated.
When I bought the house I un all new pipework as a two zone system, one for upstairs and one for downstairs with 2 thermostats that can be controlled together if needed. I could further expand on this by fitting zoned radiator -Wiser, Tado or Hive if needed.
If I forget and leave my heating on all night in the winter it would cost a third more based on the – 8hr work 8hr play 8hr sleep saying. Like @Oscarmax I gradually increase the temperature throughout the day to a point it prevents my Raynauds occuring.