For things that need to be stand-alone I'd first check if there's an existing off-the-shelf option first which generally would be more cost-effective to buy and look better than anything I could make myself.

For temp sensors specifically I generally just go with whatever off-the-shelf stuff is supported by this firmware: https://github.com/pvvx/ATC_MiThermometer - as a bonus they can run on battery for a year or more.