I wanted to add CO monitoring to the display, as it should be very easy and would be another way to track CO.  I originally bought the Adafruit MiCS5524 CO, Alcohol and VOC Gas Sensor.  Turns out that chip is 5V and I don't have 5V available.  I could use USB voltage, which would require plugging in which I'd like to avoid.  Or I could get a voltage booster, like the PowerBoost 500 Basic - 5V USB Boost @ 500mA from 1.8V+.  Then I would have to do a voltage divider to ensure the output was within what the Feather can handle.  Doable.  But at that point, I could really just get a 3v VOC sensor.  

3V compatible VOC sensor options:

Adafruit sells the Bosch BME688 which also senses temperature, pressure and humidity.  Temperature and pressure would be nice.   Uses I2C.  Current consumption (peak) 3mA

Another alternative is the Adafruit SGP40 Air Quality Sensor Breakout - VOC Index for $15.  I2C interface.  Current consumption 2.6mA.

So, we need to make provisions to solder the gas sensor into the I2C connections that will be shared with the OLED display.