This looks comfy in certain work conditions

I do love when furries try to work out specifics of the universe we're all invested in. In this case, tension rings are a really great solution, but consider also the difficulty of like... how tensioned those rings need to be, in places that are difficult to reach. Maybe you could slip some off (certainly at the tail), and slip the whole thing off like trousers. Consider also a cloak? I mean, it wouldn't get in the way of the backfin but would keep the sun/snow off of it.

I think a cloak would be a good next thing to draw

This feels like formal wear to me. Putting the rings on would be relatively laborious and they would necessarily grip the body fairly tightly in several places. You're trading fin comfort and mobility for having rings stuck to the rest of your body. So think like ties and corsets and bras, garments that are tolerated because of certain functionality or social expectations but which people often dispense with given the opportunity.

Different methods of securing the rings could track with development of social attitudes or fashion as well as technology. Maybe once upon a time the fins were regularly pierced to allow the rings to join, a practice now seen as barbaric or outmoded. (Certain people might still do that as a fashion or social statement.) Magnetic attachments feel like one of those clever and technically functional ideas that never caught on or became fashionable. Flexible tension rings feel the most "modern" solution.

Actually you reminded me to look a little more into topology of their body surface because I'm fairly convinced there may be a way to cover almost everything without compromise, although it would take fairly elaborate garment construction. I'll work on a ring-shaped cloth that goes around their neck, over shoulders and under their tail/between their legs, and possibly a thin cloak going over the tail for minimal irritation or fin-covering social formalities - or none where it's not needed.

I'll work on that probably tomorrow. I also do have a third sketch I already made which I think could be elaborated upon!

Ooooh, love this. I've had this connundrum with a GURPs character once and how she put up with it was to not having anything going on towards the tail where her fin was more pronounced, and just the fin pressed back (flexible fins) with a loose, tied, slit in the back of their jacket for any particular pointy bits to not run through the material itself.

For them, the frills and fins were growing larger as a part of apotheosis into a dragon - and it also made it increasingly inconvenient to wear belts and anything else that needed to interact with the tail or lower back. They ended up just belting everything they would normally hang on a belt to their limbs, but perhaps a fitted waist ring would be a more elegant solution!

Note: character was an amphibious kobold.