I would use this one. https://www.adafruit.com/products/38...dnQaAm5k8P8HAQ
There is a lot of support available for it so writing a sketch to put the parameters on OBD2 shouldn't be hard.
Also the most likely reason you are having variance in FE with humidity is the effect on detonation the water in the air has. Your engine can advance more timing with humid air compared to dry air. There used to be a trick involving a bubbler and a mason jar with water that was popular for preventing detonation, but I've never tried it myself.