Oil heaters are horribly energy inefficient, they play havoc with your electricity bills. I think OP should see what their house is equipped with before buying if they dont already have oil heater.
We have both aircon heating and then radiators upstairs in the rooms. Upstairs we only put them on in the late afternoon then put them low over night and off when we get up, though the tortoises room has one on constantly with the door closed. They can't be left outdoors at grass all year too cold, they came in this week and will go out again in April.
Heating is only maybe not necessary if you live in Central (for example) and your flat is well insulated. Where we are in the country park it's always at least three or four degrees colder than anywhere in the city.
I would love a fire place. One of these days Im going to knock a great hole in the wall build a chimney and put in a lovely fire place. Add to the fossil fuel burn up
I grew up in a very hot country, though nights were always lovely and cool. I also lived in Northern Europe and the UK all the houses have double glazing from the oldest to the newest. Even Ludwig's faery palace Schloss Neuschwanstein in Bavaria has ancient double glazing. Hong Kong not, don't know why but it would certainly help in summer and winter.
The sun gets weak and cold in winter so not a guarantee your house will be warm. It gets pretty damn cold enough here enough to make you want to stay in bed, so heating is honestly yummy and not a luxury!