Barth,
you might consider buying several (2-3) humidity sensors instead of 1, because sometimes in high humidity enviroments (especially when there is condensing humidity) the humidity sensors tend to saturate and then read overly high values. They usually recover after a few days in drier conditions, but sometimes they do not. I have a good experience with Sensirion humidity sensors SHT31 for example:
However the best humidity sensors have a PTFE membrane which blocks excessive moisture from getting onto the sensor membrane, I have to say that after purchasing Atlas scientific humidity sensor:
I’ve had consistent humidity readings even in high humidity enviroments and I highly recommend this sensor. It is quite cheap for the high quallity and robustness.