I have a guppy pool. It's a no brainer. Though I started out with a tropical fish pool, thanks to guppy breeding habits now most of the fish are guppies.
That doesn't mean the other fish died though. I have a bunch of different kinds, and apart from dying of old age seem to being doing as well as the guppies, and one egg layer has mastered reproducing on its own in the pool. LOL
It's a tiny, native fish called Bluefin killifish which grow longer but , because they are a bit skinnier than a male guppy.
They are trouble free killifish, and the males are very colorful.
They don't require any special handling like other killis that need some dry time to reproduce Etc. and live as long as guppies.
What you want to create is actually very close to ideal conditions for those guys.
In fact the person I bought them from kept them alive during the summer in mop buckets. They are swamp fish and can easily survive conditions that would kill most tropical fish.
I've had neon tetras in there for over a year as well.
Despite their reputation for being delicate, I have found them to be as hardy as the guppies surviving all sorts of accidents as I changed things to find the right set up for me. They are supposed to die when water drops to 60degrees, but they survived that a few times (due to a heater mishaps in winter).
In fact I have a variety of tetras in there, and they all seem to do rather well, and much better than my experience putting them in an inside tank.
It makes me wonder if their reputation for being delicate has far more to do with being unable to cope with the extreme water chemistry that is an aspect of keeping them in 20 or 30 gallon aquariums more than actually being simply delicate.
In the pool I'm guessing the much greater ability of a much larger volume of water to buffer such things and prevents them from exceeding their tolerance.
IF YOU WANT SMALL and active
get bumblebee gobies, and no they don't need a brackish set up. People seem to think brackish means something distinct from fresh water, but that's not exactly true.
They also have done quite well, and are constantly patrolling the pool as if they are the sheriff and deputy always on the look out for something new and unusual. LOL
The brackish water that many guides say fish like puffers, bumblebee gobis and dwarf mud crabs require would be "freshwater" to our senses, because were we to drink it, we would NOT taste salt at all.
It's also fresh enough for freshwater plants to do fine.
An example of a brackish river is the Texas Brazos river. If you ask people who know of the river however most would say it was a freshwater river, and think you were crazy to call it brackish since that's where the city of Waco gets its drinking water without desalinization. LOL
Only when I added some dwarf mud crabs did I add a minuscule amount of salt.
Also at 1" pygmy sunfish might do great. Since they are native they can tolerate extreme conditions with little effort. Males are beautifully colored and far more likely to thrive with far little effort.