The Aranet4 device is a non-DIY CO2 sensor however it operates over Bluetooth instead of Zigbee, not sure how much of a deal breaker that is for you. I had no t

The Aranet4 device is a non-DIY CO2 sensor however it operates over Bluetooth instead of Zigbee, not sure how much of a deal breaker that is for you. I had no trouble hooking it up to my Home Assistant setup though, and the device is fairly affordable (for a "proper" CO2 sensor that is, not one of those Ali Express devices that estimates CO2 by VOC measurements).