A lot of people use some variation of this humidifier. You don't want to get one too smart, because you want it to turn on and off with power cycles. You don't want to have to push a button when power is restored from your humidistat.

I use this one, and as an added benefit, you can get some cheap hosing from Home Depot and jury-rig it so that the mist goes through the hosing into a hole you drill into the side of the fridge, which saves you a ton of space at the bottom of your mini-fridge.

https://www.amazon.com/Crane-USA-Humidifiers-Ultrasonic-Filter-Free/dp/B001ADL1SG?ref_=fsclp_pl_dp_9

And if you get fancy and want a dehumidifier as well for exacting humidity control, this is a tiny tiny one that easily fits in the bottom of a mini fridge. https://www.amazon.com/gp/aw/d/B07D2HV8NK?psc=1&ref=yo_pop_mb_pd_title

This one, although the price looks like it went up: https://www.amazon.com/Crane-USA-Cool-Humidifier-White/dp/B001ADL1SG