BeLight tells me that Labels & Addresses still works fine in Mojave, but as a 32-bit app, won’t make the jump to the next version of macOS.
As a replacement, they’re pointing users to their Printworks app. It does labels, but I don’t yet know if it can do one-off labels on a printer like you’re talking about. I have a Seiko label printer somewhere so I’ll see if I can give it a try.