And ESPhome works very well together with Home Assistant if you want to build stuff yourself.

Just get an ESP32 and a sensor or other device that is supported by ESPhome and you will be able to program and connect it very quickly.

There are also ways to use sensors that are currently not supported by ESPhome by writing a custom component, but that is something that I don't do, too much effort and it's not that easy.

It's also crazy just how many different devices can be connected to Home Assistant. If it is at least somewhat widely used chances are good that someome has already written a plugin to make it work.