They've had a 12v version for a while, and it's quite nice despite the high voltage requirement. I made a little breakout with a boost converter. Sensirion has

They've had a 12v version for a while, and it's quite nice despite the high voltage requirement. I made a little breakout with a boost converter. Sensirion has a slightly smaller sensor as well, SCD41 that I think works on similar principles. Neither are cheap, around $25-40 each in small quantities. The infineon one has a full blown microcontroller handling the operation of the sensors. To keep accuracy you would need to have a CO2 gas setup which isn't cheap either, but for indoor use I don't think it matters.