I just ran across this thread randomly, but there are lots of devices out there that will do what you want (measure the humidity) as well as lots of others that will control the power of the dehumidifier. The key is how you control the whole thing.
Let me shamelessly plug an app I wrote and have been using for over a year:
In this case I use my Halo fire alarm as a humidistat and the Zooz appliance plug. Works great with the app to run only as much as needed and now I just leave the setup running year round. I’d say pick whatever device that you like to measure the humidity as long as it is located appropriately (not near the dehumidifier, not near a door or window, etc.).