Lastly I was looking ar Heiman CO2 sensor (Zigbee), but I haven't decided yet :
I also have Eurotronic (Z-wave) which reports also VOC, but I had it switched off for quite a long time, due to some z-wave mesh problems that I had with a lot of FLiRS Z-wave devices. I will try to put it back in operation next days.
From the same link you can also check the MCO HOME which seems even better quality, but double in price.
