Behind every perfectly tailored “Bridgerton” costume and ad for Lululemon leggings lies the work of fit models, the unsung heroes who help designers create clothes that actually work on real bodies.

So, you got a 3D printer for the holidays, and you’re excited to dive in. Chances are, you’re not sure where to begin. What can you print? What’s fun? What’s useful? Justifying the purchase of a 3D ...