Some time ago I have purchased online carbon dioxide (CO2) sensor module MH-Z19b. It's a cheap and very simple sensor with the UART interface allowing concentration measurement in the range up to 5000ppm.
Part 1 - Hardware design [/2019/06/10/carbon-dioxide-sensor-mh-z19b-part-1/] Prototype projects do not require complex software and I am using the Arduino framework because it has plenty of useful libraries for all possible device types. For compiling the project I am using PlatformIO framework.
Recently I have purchased one more carbon dioxide sensor module - CJMCU-811. The module is built on a chip CCS811 by company ams.