I'm not sure why I addressed my post above to Steff, when it should have been to Susan! It must be late!
I don't bother with a duvet at this time of year, Susan. (Yay! I got your name right this time!). I simply sleep under a nice, big bath sheet. I find it's just the right weight for keeping me warm without feeling oppressive.
I'll probably go to bed, and try to get to sleep, soon myself but there's a blackbird that is determined to keep me awake every morning!