I use Awair Element to monitor temp, humidity, co2, pm2.5, voc. It seems to be sensitive, accurate, and stable as far as I can tell. Fresh air co2 =400pm. Detects the other half with her creams and potions and quickly detects co2 rise when someone enters the room. It’s not cheap!! It has a phone app and API possibilities. It calibrates when the room is ventilated and has built-in fan to force air over the sensors. The fan is a bit noisy for bedroom use and sensitive ears. Mains powered, no battery
Here is the write-up I made on how to get the data into openhab and Grafana