I've often only had a single heat source in one room. Random tips:
Layers of clothing, always. After years of this, I'm in head to toe woollens - hiking socks, thick leggings, vest, long sleeved top, massive ancient jumper, fingerless gloves, hat. Standard indoor clothing in winter. Any spending on summer clothes only happens after warm things for the next winter. Felt or sheepskin houseboots are a worthwhile investment if you have wood/tile/slate floors. Solid soles last longer.
Rethink usual routines. A hot bath/shower at bedtime makes it easier to sleep in a cold bed and unheated bedroom. The key to surviving an icy bathroom or cold water is keep your hat on in the shower 🤣 and feet straight into socks/houseboots afterwards. (In winter, hairwash days are detested as get-wet-all-over days).
Unheated kitchen. Food keeps much better in a properly cold space (though olive oil is treacle). Most freezers won't work properly below I think 10°/16° so be prepared to target heating when it's really cold, or have a contingency for the suddenly defrosted food. (I daydream about having a proper freezer or fridge freezer, but there's no point without heat to keep it working).
Knife safety! Be very careful preparing food in an unheated kitchen - frozen fingers in a cold space are numb and unresponsive, it's easy to cut yourself.
Putting permanently cold fingers into sudden heat eg. hot water or hot oven result in what I think are chilblains, which hurt like mad for the rest of winter. So try to buffer the temperature change.
This last one is really hard when you're already cold and hungry, but forcing yourself to make giant pots of thick wholesome soups/stews/casserole really will keep you feeling full and warm for much longer than the faster/easier options. (I say this after a week of eating crap and feeling worse for it).