The first time I encountered a duvet was at my Norwegian boyfriend's house. I was so fascinated that we went to Ikea so I could get myself one.
I'm now with a better duvet and
much better boyfriend

and I wouldn't trade either.
I've bought cheap duvet covers for my cherubs' comforters when they were getting ratty and that worked rather well. I have several duvet covers and it's nice to change the look of my room with something so simple as changing the cover.
My cats love the current duvet cover, which is brocade on one side and cotton on the other. I do, too!