We have two duvets: one filled with goosedown, and the other filled with silk.

Our bedroom is on the lee side of the house, which has nice modern forced-air central heating, and I find the goosedown duvet too warm. It now has a regular gig in the guest room, which is on the windward corner of the house and consequently rather chillier.

The silk-filled duvet was advertised as just the thing for middle-aged women prone to night sweats, and it has proved excellent: not too warm, and definitely warm enough -- except on the occasional night when the temperature drops to minus lots and lots with a strong wind from the east. Then I get out the old Hudson's Bay Company blanket and flop it on top.