Grab any 1950's "how to be a good housewife" book, use a bit of scripting to replace "housewife" with "housekeeper" and "husband" with "partner", and republish.
I never had a duvet until the late 70's. I had heard that Swedes slept under duvets, but we had to settle for blankets and sheets. I ws envious! Well, we did have what we called "eiderdowns", which were like duvet inners, but lined in a heavy satin. But they were used as throws for extreme weather; you still slept between sheets and blankets.
I think my parents' generation viewed duvets as unacceptably decadent, and thought all children should learn to fold hospital corners[0] to build character.
I must also add that duvets were created for cold rooms and they're great for that: feeling so cozy warm when your nose is still chilled... However you get them as only choice in mostly any hotel nowadays, which also heat the rooms at 22C or more, so sweating and a general sleeping discomfort is guaranteed. Or shortly put: I hate you hotels with duvets.
Would also highly recommend! It's not quite exactly a practical handbook, and doesn't cover topics such as duvet cover changing, but it is considerably more relevant than most popular science/mathematics books. The very first chapter, for instance, covers the idea of explore/exploit choices, and does so in a way that is both general enough to be genuinely useful in everyday life (at least at a conceptual level) and mathematically rigorous enough not to throw you off should you want to read further.
I taught my mother how to fold a fitted sheet. A girlfriend taught me and I was floored at how elegant it is. Prior to that, they just made me angry and ended up in the closet in a wad.
This is what I do. I take a corner of the inner and stuff it into the outer until I find the corner of the outer. Then I try to keep those two corners in place while I do the same with the other corner. Then I grab both corners from the outside and do a lot of vigourous shaking until everything lines up. It takes ages and doesn't always work. I think I will try starting inside out from now on.
IME neither inside out nor the method you describe work well and both are tedious. Inside out does not work well, because the cover doesn't obey gravity and refuses to fall down to cover the duvet completely. It is a secret power of bed sheet covers. That, or it has to do with other things like friction.
I do a modified version: I put all the corners in the right places, then a good shake by holding two adjacent corners straightens everything out. May not work so well for duvets much wider than your arm span.
I do that and while the shaking is unpredictable and often requires doing it from multiple sides, I find it a strong but strangely pleasant exercise for my shoulders.
