Using original 250 GB SSD as an external boot drive?

I hope I’m not the only one who still loves and uses a mid 2012 15’ Macbook Pro retina!

Some time ago I bought a Samsung EVO 860 1 TB SSD to replace my original internal SSD. I had to look around for adapters, but I got one that seems to work reliably (whenever I’ve tested it) and has good tolerances.

However, I’d like to find a way to still use the original 250 GB SSD externally, as a boot disk. I’m currently running 10.14.16 Mojave and would roll things back to an earlier OS on the smaller drive.

It’s hard to find a decent enclosure. Following other posters I came across the OWC Envoy Pro, but I can’t see for certain whether anyone used their SSD in this enclosure as a boot disk. Can anyone verify that this works?

Or do you have any other recommendations for a decent enclosure, that ships preferably from the EU?

Thanks for any and all responses!