Why hasn't anyone done this before?
There are no household chores I dislike more than washing my duvet cover. It's not even the washing bit that really bothers me—it's the drudgery of getting the cover back on the duvet.
Four-year-old Canadian mattress-in-a-box brand Endy gets it, and have expanded their lineup of get-good-sleep products to address the issue. The new duvet ($270 for a Queen, at endy.ca) and duvet cover ($135 for a Queen, at endy.ca) were designed to mitigate common duvet annoyances.
Matching Endy logos on both the duvet and the cover make it easy to identify which way to align the sheets, and snaps in each corner prevent the duvet from bunching up inside the cover. I also found the snaps to be helpful in getting the duvet into the cover; once I snapped in the top two corners, I shook out the cover and everything just fell into place.
The Endy duvet is made of machine-washable (key), hypoallergenic (very key) Phase Changing Materials (PCMs), which are synthetic fibres able to absorb and release thermal energy to regulate temperature. The cover is a super luxurious feeling 480 thread count sateen weave cotton.
Prior to trying the Endy, I was using a natural bamboo fibre duvet. I loved the look and feel of it, but didn't realize how cold I was until I made the swap, and felt significantly cosier and more relaxed. (Bamboo is super soft and lightweight, but apparently not up to the warmth needs of a Toronto winter.)