Hi @momalley ,
I’m Richard - CRO Expert at PageFly Landing Page Builder. Welcome to Shopify Community!
Regarding this, you can refer to some print-on-demand apps such as EPROLO POD, SPOD, etc These apps are friendly customizer and users could see the preview of their customized name.
I hope my answer will be helpful to you and hope you will find the best one for your store.
Best of luck!