Print with PETG to allow for some temperature tolerance. I used JAYO black PETG.

Has space for 3 5mm x 2mm round magnets, available here. The magnets require some force to be clipped in. If your filament has noticeable shrinkage you should consider printing a slightly upscaled version.

Compatible with these thermometers / hygrometers from AliExpress

Remixed from @Arek on Printables. Note that they used a GNU license, I replicated it as close as possible using the CC options MakerWorld gives us, but please read the original license details if you plan to publish or remix this model.

(AliExpress links are affiliate links, meaning I get a small commision at no extra cost to you)