I don't think that "one size fits all" on the Zafu.
Everybody ... every body ... is different. It really is just something to sit on comfortably, with some support, balance and stability, and then forget about.
I do want to recommend this book again to all our sitters, especially folks struggling with posture a bit. Also some Zen folks can be quite obsessive about getting the posture "right," I am more fluid in my views toward posture, much as this book discusses.
Book Recommendation: - THE POSTURE OF MEDITATION
https://www.treeleaf.org/forums/show...-OF-MEDITATION
Most Zafu, in my experience, are between 5 - 8 inches (150-250 cm) off the floor which should be perfectly fine for individuals of almost any height. Bigger people usually benefit from a bigger cushion, and small people from a small cushion. It is best not to be too high because you’ll be sitting at a forward angle most of the time and your knees should be able to touch the floor.
This is one reason you may wish to get a buckwheat cushion (or make one!) and experiment with the quantity of stuffing inside. Same with a seiza bench (which, by the way, is also pretty cheap and easy to make with minimum woodworking skills, and a quick trip to the home improvement store.) Then, you can experiment with raising or lowering a bit until it "feels okay."
However, most important is not to
obsess and fetishize the cushion, and getting it "just right."
Frankly, there is a tendency in some corners of Japanese Zen to obsess about getting the posture "just right." This is a concern not generally found in other flavors of Buddhism and meditation in other cultures in Asia. To make a long story short, throughout Japanese culture (not only in Zen) there is a lovely fixation with "proper" form. It is wonderful, and leads to everything from baseball to tea ceremony that is very beautiful. However, it also can lead to certain powers and unsupported (pun intended) physiological attributes being attributed to precise posture, e.g., that it results in certain mysterious Ki and like energy flows in the body. Baloney.
Middle way here: There are balanced ways to sit which are comfortable and do not cause pain, and unbalanced ways to sit which are uncomfortable and cause pain. Every body is different, find the comfortable way for you then ...
Find a comfortable, stable and balanced way to sit that lets you sit for long periods. Realize that it may need a "tweek" now and then during the sitting period as the body settles ... then forget about it, and just sit. There is no more a "proper" form for sitting than a "proper" form for riding a bicycle on a Sunday afternoon. If it feels right and comfortable, it is.
Here is Taigu's always very wise and common sense advice on using and purchasing a Zafu ...
Gassho, jundo
STLah