Draft exlcuders - you can make your own cheaply or buy them,.
Natural fibres - saving to splash out on wool duvets but I also have my grandma's wool bed blankets and honest to God they're amazing! Naturally temperature regulating so I was using a cellular one in place of a summer duvet until the heatwave kicked in.
Brushed cotton sheets.
I also want to get proper wool throws for the sofa.
Slippers - sheepskin ones for the reasons above!
Wool or wool blend socks - so much warmer than anything else I've used and more comfy than thick fleeces ones.
Getting out for a walk or going somewhere every day makes a huge difference too, even just 20 minutes out the house.
Cover vents but uncover them in spring and summer.
Hang muslin curtains at windows too. Theyre sheer so you'll still see out/let light in, but they fibres are thicker than polyester voices and the gaps in the weave will help trap air. They won't make a huge difference but if you're worried about drafts and want extra protection around windows, they'll help.
Include complex carbs and (if affordable and omnivore) meat in meals - body produces more heat digesting these.
Hot shower to warm up if you get chilled.
Rugs on hard floors. Sheepskin rugs by bed or sofa and great for pets to keep warm as well. Make sure they're real sheepskin though, not fake.
Install loft insulation if you can.
Have sex.