When in doubt Google. For me, a definition is the source of truth.
I love to change bedding and paint. About 12 years ago I did not know what a duvet cover was much less a duvet. Discovering the duvet cover has changed me from a comforter person to a duvet person.
Over the years we have received emails from customers who are upset because they ordered a duvet cover and expected a comforter. I feel their pain and do my best to help the customer find happiness.
My suggestion is that you purchase a good quality Duvet and a Duvet Cover. Make sure the duvet cover has inside corner ties or, if not you should add them to your duvet cover. The secret to success is using inside corner ties and securing the duvet cover to the duvet. Purchase a machine washable cover and you can remove for cleaning as needed.
No more removing the comforter before you go to bed. No more adding layer after layer on your bed. I would recommend that you purchase a white duvet so the pattern does not show through your duvet cover.
Below is a definition for the dictionary Wikipedia.
A duvet (UK: /ˈdjuːveɪ/, US: /duːˈveɪ/; from French duvet [dyvɛ] 'down') is a type of bedding consisting of a soft flat bag filled with down, feathers, wool, silk or a synthetic alternative, and typically protected with a removable cover, analogous to a pillow and pillow case. Sleepers often use a duvet without a top bed sheet, as the duvet cover can readily be removed and laundered as often as the bottom sheet. Duvets originated in rural Europe and were filled with the down feathers of ducks or geese. The best quality is taken from the eider duck, known for its effectiveness as a thermal insulator.
A duvet cover is a cover for duvet. The duvet cover protects duvet during use.
Duvet covers frequently have a decorative function on the bed, allowing for change of pattern or design for different occasions, or to serve different functions; for example, a heavier duvet cover may be used during colder seasons.
Mass-produced duvet covers are usually made of cotton or a blend of cotton and polyester and can be easily removed to wash at home, while a duvet can be expensive and difficult to clean. Duvet covers may be made from two sheets or panels of cloth sewn together.