Arduino + CO2 + humidity + noise + temperature sensors on one board
For humidity and temperature you can plug the DHT11 or DHT22 to your arduino. DHT11 is cheaper but you'll get a more precise value with DHT22.

For noise you have ready made PCB like these : here
You'll only have to plug it to GND, 5V and analog input.

For CO2 this is more complicate. There is a cheap but very unprecise option, using a MQ135 sensor, here is a tutorial: here
Otherwise there are better sensors like the K30 but they are much more expensive.