Although I live in an old property (over 100 years old) it has been made as thermally efficient as possible. I believe in as many passive and non technology methods as possible. These include open solid fuel fire (back-up) to avoid condensation by providing natural ventilation, Conservatory with thick insulated concrete floor to reduce peaks in temperature and provide thermal store.
Installed Solar pv to reduce carbon footprint and dependancy on the grid (weather permitting) and as an investment.
More recently installed air source heat pump again to reduce carbon footprint and dependancy on the grid.
Most cost effective measures are to improve thermal performance of property with good insulation generally but watch natural ventilation/airtightness to avoid condensation problems unless installing a mechanical ventilation system.
Use as many passive measures as possible to reduce reliance on technology, maintenance and break downs