This wall mount for a switchbot thermometer has a few design choices I think make it pretty good:

1. it has drainage holes
2. it only needs one mounting hole
3. it has a second piece that make it stand off from the wall/etc so it's taking the temperature of the environment and not that of the wall which may be leaking heat from building
4. it hugs the sensor well, but still shows off the majority of it, as it is a good looking product

P.S.

I made this using eSUN Black PETG so it's a little stronger and has a better chance against the outdoors, if you're using it indoors though PLA is absolutely fine.