I wear 3 pair of socks and thermal slippers all year round. I know its not the thick duvet that warms them as they warm if I lie anywhere.. So I'll follow your thread to see what advice you get.
Thermals or pyjamas make a big difference diespite being so thin. I've suffered from cold extremities all of my life and find that apart from clothing, a good brisk rub works wonder.
As far as winter goes, a young lady in an outdoor shop set me on the right track as far as hand/foot warmers go too. Don't grip them or put them either side of your feet but put them on the back of your hands inside gloves or on the top of your foot inside your sock. It warms the blood on the way to your extremities (apparently).
I have found that socks, brushed bedsock type, with hardly any elastic on the tops, keep my feet warmest, worn together with fleece jogging bottoms (M and S) - as a person who suffers from the cold - thus speaks the voice of experience. Always have an electric blanket to warm the bed up, never get into a cold bed.