i would use straight well water, if i had access to a well. even if it is hard as rocks. my water is also about 20 degrees hard, from the tap. but it's been down at about 260 mg/l recently.. which is backwards, it should be getting harder as winter comes here..
most of the gh from ground water is a dissolved micronutrient solution.
i have angels, plecos, shrimp (caridina and neocaridina) as well as easier spawners like cory cats and live bearers all gettin' it on and making babies in my hard city water, i don't make an effort to raise the eggs but have seen at least a wiggler of everything but the aforementioned angels.
but i think they're only just past their second spawn, they are young still.
as far as plants go, the only plants i have tried and failed with are seusswassertang and l. brasiensis.. neither of which had anything to do with the water params AFAIK
.. okay.. i killed a banana plant once too..
they say aponogetons are soft water only plants, i've had a few over the last couple years THRIVE, i had an ulvaceous hybrid with leaves the size of an amazon sword where it grew. none of the other aponos have done bad, they're just a bit lack-luster compared to the crazy ones.
most plants available and traded in the hobby are incredibly hardy, don;t be afraid to go walk down by the rivers and lakes to try and find some of them either. i find plants i see in aquariums all the time. eleocharis is all over here. elodea, hornwort, pennywort, some little plants that look like glosso are doing well. if you ever come across arrowhead(duck potato), that's a fun plant. it grows several feet tall and blooms white and yellow.