Some easily available, and colorful dithers, although not geographically correct, might be rosey barbs, or even white cloud mountain minnows, they can take temps down into the low 60s.
Also some of the high elevation live bearers such as Xenotoca eiseni (which I have)
and Zoogoneticus tequilla, which I've used in the past, are good.
As would be Buenos Aires tetras.
Some of our own US natives would also work, as long as not to aggressive, the Jordinella floridae, AKA American (Florida) Flag fish comes to mind.
There are also Urugauyan corys and tetras which would be very apropos.
I keep ancistrus bristlenose plecos with mine and they easily handle the 60s winter temps I use, my tanks drop into the 60s during winter without a heater.
I wouldn't think angels would work, because the higher temps they need. Those constant temps might make your balzani prone to disease, make their colors become dull, and perhaps shorten their lifespan.
The difference in providing temps tolerable, as opposed to optimum can make a world of difference in appearance.