My house has 250mm insulation in the walls and heat exchanger for fresh air, but it's still nothing compared to modern houses (mine is 20 years old). But no I'

My house has 250mm insulation in the walls and heat exchanger for fresh air, but it's still nothing compared to modern houses (mine is 20 years old). But no I'm not ever going to start wearing shoes or thermal undergarments indoors so I can lower the indoor temp by 1-2 degrees. Most of the heating energy loss in my home is probably hot water.