Here is my set up. This one is pricey initially, but checks all your requirements: Breville InFizz Fusion - mechanical (no need for batteries and has no wires), sturdy and designed to carbonate any liquid, not just water (the taste in this case is significantly better than just adding carbonated water into the drink). The CO2 tanks are compatible with old sodastream, which has multiple generic alternatives.

I also got myself a 10lbs CO2 cylinder and refill adapter woth hose on amazon, so I am refilling smaller tanks myself from it and refill the large tank once every 1-2 years in local welding supply store for $40.

I do recommend to have around 4-5 small tanks and 2 extra bottles for different sodas.

I’d argue that most wild microbes are not as bad as domestic microbes with all their antibiotic resistance development.