Shared Beds Require Separate Duvets
A large, pretty blanket laid out neatly on the bed you share with your partner can look good during the day. But at night, chaos ensues. One will be too hot, the other too cold. Worse, one of them is likely to toss and turn at night, drawing cold air under the covers. Simple solution: separate blankets.
A situation with two duvets can still look good: either fold one at the foot of the bed, or fold them on top with a large (or pretty) duvet. Thus, you can get by with smaller blankets than if you had to fit two people under them; when we switched from a queen bed to a king size bed, I kept the queen size blanket for myself. It fits perfectly across the bed, without hanging over the edge, and at night belongs only to me. (My husband prefers a light blanket or sheet.)
This technique also applies to surprise guests. If you have kids who crawl into bed in the middle of the night, do yourself a favor: have an extra blanket on hand. How to prevent them from sneaking in is a completely different question , but at least if they have their own hiding places, they will not bury under your cold feet.