A large, nice duvet, neatly distributed over the bed that you share with a partner, can look nice during the day. But chaos results at night. One person will be too hot, one too cold. Worse, one of them will probably throw and spin during the night, pulling cold air under the covers. The simple solution: individual blankets.
A situation with two layers can still look nice: fold a layer at the foot of the bed or lay them in layers with the larger (or nicer) blanket on top. You can get away with smaller blankets in this way than if you had to fit two people underneath; when we upgraded from a queen to a king size bed, I kept my queen size comforter. It fits perfectly over the bed without hanging over the edge, and at night it only belongs to me. (My husband prefers a light blanket or a sheet.)
This hack also applies to surprising guests. If you have children crawling into bed in the middle of the night, do yourself a favor: take an extra blanket by the hand. How to prevent them from sneaking in is a completely different question, but at least if they have their own covers, they will not bury themselves under yours with their cold feet.