I know a bit about CO2 sensing.
Is this a one off or mass production application ?
Do you care much about power consumption/size/response time ?
I can't really advise you much without this information.
Both the humidistat and CO2 measurement is a new thing to me and my team, we are all students and this is our final year project.
What is your project ?
Try Gas Sensing Solutions (www.gassensing.co.uk) for the CO2 sensor.
I think you will have to do humidty separately - look at Farnell 1784720 for a voltage output device at a reasonable price.
My project is a remote enviornmental measure, where the sensors will send in the voltage to my microcontroller to transmit the reading via RF to my receiver at a distance away and print onto the LCD screen.
My project is a remote enviornmental measure, where the sensors will send in the voltage to my microcontroller to transmit the reading via RF to my receiver at a distance away and print onto the LCD screen.