AcornA10080 womens Moc

Are these slippers all synthetic? Are they vegan? Thanks!

All of my Acorn Slippers I have bought an 8-9 as my shoe size is 9 or 9.5, a lot of people say to size up with others saying size down? 🤷‍♀️

Are these supportive at all?

I'm trying to order acorn women's moc. (essentially a pair of slippers). i can't find anyway to select size? i must be missing something obvious.