Add oxygen generator as a separate device, rather than get infinite oxygen so long as your base is powered. Maybe need more than one or even a larger generator for bigger bases, coupled with an oxygen gauge similar to the power gauge. Also, a power inverter or similar device to convert the various forms of energy into electricity. Power is way to simple in the game.

similar idea, though i would sperate it into new a game mode for those that want a immersive and challenging experience: https://subnautica2.nolt.io/10069