Sasaferrato
Super Refuser!
I've got an 1850s rab (stone/clay/stone) house with 2-ft thickish walls which even though in Cornwall was bitter in winter when I got here. The rooms were too small for baton-type insulation so I've put up insulating wallpaper. Only cost a couple of hundred quid and relatively easy to do once you've got the hang of it.
Fair amount of wool loft insulation plus secondary glazing (only a couple of houses with wood sash windows left in the road) using magnetic strips. Again pretty cheap although getting the measurements right was hard because all the windows are different sizes and a bit wonky.
Not sure how effective objectively but it's certainly taken the chill off. Conservatory warms the rest of the house up for most of the time, with wood-fired Rayburn heating for four-five months in winter and a 1-kW electrical fan heater upstairs when it's particularly cold.
Certainly wouldn't be good enough for a lot of people who seem to like 20 C all year round but I grew up in uninsulated house with coal fire, and get a headache in proper centrally heated houses anyway
When I were the lad, the living room was the only room heated. You had ice on the inside of the bedroom window in the Winter.