I've been very happy with my AirGradient [1]. It measures PM2.5, CO2, temperature, and humidity. I got the $67 kit and assembled it; it was a fun soldering project. I like that I can reflash it and get it to send data to VictoriaMetrics on my Raspberry Pi over WiFi. The biggest thing that I dislike is that the CO2 sensor loses calibration over time and (from what I understand) needs to be re-exposed to fresh outdoor air every ~2 weeks.
I might buy this IKEA sensor too to see how they compare; wouldn't hurt to be able to monitor a second room.