Do you have access to a printer that’s big enough for a torso? That already feels like a huge expense to me.
You mentioned leather and that seems like the easiest to manufacture and adjust.
I did a quick search and this came up, super affordable and probably something you could mod and build off of easily
https://www.amazon.com/IFKODEI-Trainer-Corsets-Shapewear-Slimming/dp/B09HCGN3N8
Take the corset concept and sew on a strap diagonal from the bad nipple over the opposing shoulder?