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 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.