I’m totally a novice as well, I went to the leather store here in Portland (Oregon Leather) and bought a half-a-hide of veg tanned cow leather. I don’t recall what weight they said it was, but I’d say it’s probably medium-to-thick. I’ll ask them next time I’m there (this weekend probably).
My wife has since made 2 more of these, one of which she dyed a nice deep blue. Looks really great.