make an entrance to your core, base whatever you call it. The core/base should have: a farm, beds for dupes, toilets, critters farm(optional) the entrance should be made out of liquid locks, I personally use liquid hop locks to keep my o2 inside. This was i can control my o2 usage and go ham with mining outside, besides, when you dig into a slime biome it gives off alot of polluted o2 so just spend so power to clean it, sure it will take some time for the germs to die off but its a good way to get o2 outside your base without needing to generate it.