Like others have said, ZigBee is the way to go for low-traffic things like temperature sensors. It uses a lot less power than WiFi, so battery-powered devices can last for months on a CR2032.

I've got some Aqara temperature/humidity sensors that I have hooked up to my Smartthings Hub and then imported into Home Assistant through the cloud, but you can use any ZigBee adapter that works with Home Assistant: https://community.home-assistant.io/t/using-aqara-temp-and-humidity-sensor/408166/9.

I also recently got some Sensibo Elements boxes, which are wall-powered WiFi air quality sensors that include temperature/humidity. They have an official HA integration. If you go for them, don't worry about the sale countdown on the website; it doesn't actually seem to ever end.