Welcome to the forums! Without pH, GH/KH (and ideally TDS) values of your well water it would be hard to steer you towards or away from your easiest water supply. I keep most of my tanks on tap, but have a couple that get remineralized RO/DI only. It largely depends on the water coming out of your faucet and the flora and fauna you wish to keep. But you must by all means bypass the water softener if you are going to use it in an aquarium. I use a SpectraPure RO/DI unit myself, and don't bypass the DI. And I probably drink my body weight of it every year too, technically speaking. To my understanding, the worry is that is so "hungry" and devoid of any minerals that it can strip the body of these things. But I use it as my main source of coffee and tea water. It's great for that! You don't want to make it your main source of hydration, but it's far from poisoned or anything. I'd certainly cook with it. But that tangent aside, lots of low light plants to choose from, bettas can thrive in a wide range of water parameters and hopefully you have access the well pre-softener and can get some results. Your local fish store may be able to do it for you.
Nothing good happens fast in an ecosystem.