Check out this one I got .set it and good to go.. I love it ..
I like this one, needs filled about every two days. https://www.amazon.com/dp/B07R7KXHHV/ref=cm_sw_r_cp_apa_fabc_6Q62M09BEBP098MB5G9Z?_encoding=UTF8&psc=1
The easiest way to do this would be to get a humidifier that has a humidity sensor. It appears this one does, but it's 1gallon. The "mini" humidifiers don't seem to have it built in. For reliability and ease, the next best option would be a humidity controller. Inkbird is the best brand, with humidity controlled sockets for about 40USD, or something like this paired with a car humidifier.
For a one-off solution, you could either use an Echo Plus with an Aqara sensor, or Google Home with a WiFi sensor. If you use HASS on an rPi, then there wouldn't be any need for Home or Alexa, unless you need voice control. Using either wifi or Echo Plus with ZigBee, there wouldn't be any need for HASS. If you need more complex routines than Home or Alexa can provide, Hubitat Elevation can be cheaper than an rPi with a radio.
The easiest way to do this would be to get a humidifier that has a humidity sensor. It appears this one does.