I don't know how to choose the size so that the stocking would slip off the foot, but the professionals from the salon did just that. They measured everything in five places and told me — here's your size, "one hundred percent accurate." Orthopedic stockings cannot be tried on before purchase, and cannot be returned if the size does not fit. They didn't let me take pictures of the measurements and compare them with my data at home, because "you can't take pictures here, there are cameras here!" (seriously?). As a result, stockings for almost 40k drams turned out to be a waste of money. The elastic band doesn't hold anything, it's clearly not on my thigh. I hardly feel any pressure in my ankles, my already well-lived bauerfeind has more effect.
Thanks for the "professionalism" of the staff in the salon.
In the photos, the stocking is put on immediately and then a couple of minutes after.