Agreeing with everyone else so far.
Teddy fleece bedding made a huge difference to winter sleep for me (I was already doing all the other tricks like under balnkets/duvets), and once I put it on it's very hard to shift the cats from it in the day time (bonus pre-sleep bed heating!).
I sit on a sherpa fleece blanket on the settee in the day time and that makes a huge difference. (and I pre-warm that for the cats overnight
)
I also have some very heavy, hooded, cardigans lined with sherpa fleece that function like an oodie but look good enough for work calls.
A dehumidifier is essential in my town if you want to take the chill off the air (after a sunny day with all windows and doors open it was still 76% humidity in my front room the other day). It delays putting the heating on in winter, and makes it more efficient when it is on.
I already had door curtains. But having thermal black out blinds over the glass in the front and back doors has made a huge difference in winter (and summer). You can feel the blast of cold when you open them in the morning to let the sun in.
I got easy install ones from amazon. If we have the budget I want to install them on all our windows. Until then, proper thick net curtains we'll bunched up (not voiles) help take the chill off the windows very cheaply).
Our front room and dining room were knocked through (by idiots who also bricked in the dining room door) so I installed a curtain pole and heavy curtains to get back to two smaller rooms in winter.
My biggest block to saving money on energy is my husband, who when home alone is very quick to turn it on, then forgets to turn it off when he gets warm, and ends up in a t shirt and opening windows
however, divorce is also expensive (not sure how to fix that problem as he's a member of the Green party so really should know and do better).
We don't have a thermostat,
We should probably get one