I've tried the Tia with ankle strap before, yes they're pretty basic looking up close, leather isn't the nicest and marks easily. I needed a half size and they made my feet look proportionally small, something was off about it, and heel support not that great. The nu pieds do a better job, they do have a little heel and it's supportive but not super hard either where the Tia may as well be completely flat.
I've been eyeing these from Definery (if you have very small feet or larger, Yoox has quite a few for a good bit less, the only ones in my size are a questionable aqua colour) in the smooth leather brownish colour. They look to be a double layer of thick-ish leather (with hopefully some padding in between) and then a small heel and separate leather sole. Promising for a thin flat with a bit of relative comfort in theory, but I can't make out if the buckle is adjustable or just decoration. Never heard of the brand but the stockists carrying it give some confidence.
There's some interesting things I've learned about shoulders and padding in my tailoring reading. You basically have the normal shoulder pad and then depending on if you have rounded or stooped shoulders you add a little triangular panel at the back of front (or both if you want to look like a body builder on steroids, which was very popular with men in the 1930s apparently 💪). I've yet to try it (I'm slightly rounded, really depends on how well I'm keeping up Pilates) as I've no idea what ice wool is called in Dutch (I just get knitting yarn from Iceland 🤣) but it does seem like a very simple and easy fix.