I also struggled to find a reliable temperature monitoring system earlier this year. I ended up going with the Onset HOBO bluetooth temperature loggers, motivated in large part by their accuracy and because they are truly waterproof.
https://www.onsetcomp.com/products/data-loggers/mx2201
https://www.onsetcomp.com/products/data-loggers/mx2301a
During a week of initial testing, the two units I purchased agreed on room temperature to about 0.4F. Since then I've had the mx2301a outdoors and the mx2201 in the root cellar with my trees. One can upload and plot logger data to the Onset website, download data as CSV to your phone, monitor using their free app, set min/max alerts etc. I've found it pretty easy to work with the data extracted from the loggers.
This is the first year I'm attempting to overwinter japanese maples and I'm hoping to I'll be able keep them in the 30F-40F range, which I believe should be roughly equivalent to at least a few inches under sod. I've been comparing the logger data with nearby Illinois air/soil temperatures (plots below) and so far so good. Fingers crossed!