Yeah, that was a problem for me too!
The trick is to find a humidifier that has a regular on/off switch that you can keep at one setting. In our case, keep it on the "On" setting and let the humidity controller turn it on and off. In my case, I was lucky. I had an older room humidifier with the requisite switch, so I "repurposed" it for my needs.
Go to your local hardware store or home goods store and keep looking. Unfortunately, not all the online vendors show what kind of switch they use and most of the modern ones have done what you ran into - some sort of momentary button.
Good luck.
