Our village house house is warm as toast . Why ?
Double glazed windows and a 2.5 hp reverse cycle ( Inverter ) Mitsubishi split system in the main living area.
Best thing we ever did, after always saying we'll get heating next year, or saying "HK is only cold a few months"... Bugger that lol It's very pleasant coming to a warm home now, and massively cheaper to run than an oil heater/ piddly electric fan heater. if you understand C O P energy ratio's.
Install a correct sized reverse cycle heat pump split system, inverter type preferably, be warm as toast and be a lot more energy efficient... Your upfront cost will be higher, but if you knock off $1000 off your electricity bill during winter, and factor in being comfortable, the initial investment cost will pay itself off long term and more than worth it.