I've never once used a duvet cover. There are plenty of comforters that look great all by themselves. Sometimes the best solution is to remove the problem entirely.
It isn't much work, great ROI.
The other way is to eliminate the flat sheet, and have the duvet inside a regularly-changed cover, because, without the flat sheet, the duvet is in direct contact with the people in the bed.
A more detailed discussion can be found at: https://www.realsimple.com/home-organizing/bedding-debate-to...
Not eating in bed solves this and some unrelated health problems.