I actually really really want to do this! It's a chicken and egg thing: do I try to get this 1 product profitable, and then use those profits to invest in new product lines? Or do I try to do multiple versions of the product at first (which comes at higher cost, since I'd start with a small production first?)

Also need to figure out how to ship to Europe more cheaply, since right now I'm sending everything from my little apartment in Brooklyn!

Maybe printing in Europe might already help? – See www.wir-machen-druck.de, probably the most inexpensive German printery (try Google Translator). I can imagine using Amazon and its FBA service might be an option here – not sure if that's something you'd like to consider.

if you're looking for printing services in germany: https://www.druckpreis.de/

and it appears they have at least some info for some other european countries :-)

disclaimer: not affiliated with them, though i did some work for them a few years ago