Nothing wrong with candles or oil lamps indoors, they have been around for centuries. Just be mindful of them. My kids have no idea on how to properly trim a oil lamp wick, but I do and I am only 49.

We so often rush to discard "old" technology for new just because it takes practice/experience/diligence. Maybe we should just practice more.

Propane camping stove indoors, treat it like your gas range built into your kitchen.

My only caveat to all of this is that a battery powered CO monitor is a wise investment now that they are available.