I was looking at a couple of chairs online, and wondering whether they'd be good for stacksitting -
Apologies for my slow response!
I took a look at the chair in the photo and it seems to be pretty helpful for stack sitting. It does have a pelvic tilt that you can control and is high enough so that tight hamstrings are not an issue (ie. it helps to have the pelvis above the knees). It also allows for opening and tilting of the pelvis forward by bringing the knees apart. My only reservation would be that it's got a rigid structure at the pelvis opening and depending on your level of pelvic flexibility, that might or might not be an issue. If you are pretty flexible, it should be fine, but as it doesn't allow you to choose how far apart to have the legs, if you are tight in the pelvis, you might find it uncomfortable. If this is a possibilty, I would try one out before buying, if at all possible. Some of their high chairs don't seem to have this feature, but you would have to make sure that they also allow for a pelvic tilt forward. Hope that helps!