Not the OP, but I really like the SCD30 by Sensirion. It's the sensor used in the widely popular Aranet4, but the combo of sensor+MCU when you DIY it costs about a third of the commercially integrated product, so the feeling of thrifty hacker accomplishment is a nice bonus on top of the good HW.
The SCD30 also is a dual channel or dual beam NDIR sensor, meaning it doesn't really drift. Unlike most other ones that need the room to have outdoor-level CO2 once a day or week or so to calibrate.
Last year I wrote a blog post [1] about different CO2 sensors and how they work.
The best are NDIR (light) followed by photo acoustic sensors. Indoors they have very similar performance but outdoors, the NDIR (light) are much more accurate. In my personal opinion, the best ones are from SenseAir.
I used this one: SCD30. I don't have any experience with any other so can't comment on others. The SCD30 needs frequent recalibrations so I run it in continuous calibration mode and let the fan run on super low speed so it gets fresh air during the night as it sets its calibration based on the lowest ppm reading per day/week.
