>I think most of us want a pillow that keeps are head and neck aligned with our spine when sleeping on our side.
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>A duvet just sounds like a variation of a bedspread and top sheet. Which sounds like something very hard to wash. Where we just have to wash the top sheet.

No we keep the duvet/quilt inside like a pillow case. You just whip it out and bung the "duvet cover" in the washing m/c. It's equiv to 2 top sheets. Advantage is you can turn it if you wish. Often there's a different complementary pattern on the other side.