The main thing I would consider is that you want a sensor that actually measures CO2, which is usually an NDIR device. A lot of cheaper monitors and even some v

The main thing I would consider is that you want a sensor that actually measures CO2, which is usually an NDIR device. A lot of cheaper monitors and even some very fancy professional HVAC devices use “TVOC” meters and calculate a “CO2 equivalent”, and the performance of these devices is wildly variable. (The AirGradient devices are often configured with CO2 and separate SGP41 TVOC/NOx sensors. It’s entertaining to plot both raw TVOC and CO2 and to observe that they’re clearly showing similar diurnal variation, but the CO2 data is much cleaner.) Aside: the SGP41 data sheet doesn’t really recommend looking at the raw data, but you can. I have an esphome fork that does this.