Sustainability usually comes down to personal behaviour at some point, we can lobby for renewable energy, support organic agricultural policies, protest coal fired power plants but most of us are also looking at how we live our lives. Some of us make big changes, some of us make small ones. Here is one that is really easy.
Dress sensibly! When it is cold wear layers, even in the house. This will enable you to use less fossil fuel to heat your house. You can turn your thermostat down. One of my personal axioms when I go camping, climbing, walking, whatever, is that it is always easier to stay warm than to get warm, just as it is always easier to stay dry than to get dry. Stay dry and warm and you will need to expend less energy getting warm and dry. This applies in the household as well.
I'd like to suggest that you extend this to teaching others how to properly layer clothing for maximum warmth. This is particularly important for the elderly. Every year in Britain thousands of pensioners die of causes related to fuel poverty. They can't afford to heat their homes properly. Many use blankets to stay warm but when they move around are not dressed properly. Every winter my wife and I have to remind her mother to wear sensible clothing both when she goes out and in the house. She'll turn on the heat while wearing a thin cotton short sleeve t shirt and thin acrylic cardigan, no long johns, no cap. Meanwhile I'm wearing long johns, fleece pants, a long sleeve heavy cotton t shirt, a fleece overshirt and quite often a cap. Old habits die hard, if we weren't there to remind her, as we won't be next winter, she would wear what comes out of the drawer instead of searching for the right clothing for the conditions.
No matter how many times we suggest it I don't think she will ever wear a cap indoors. Like the lady in the picture she is more concerned about how her hair looks than her heating bill, thankfully she doesn't wear pearls. This not something we expect to change but we can set an example and gently encourage her to bundle up.