The SONOFF Zigbee Human Presence Sensor (SNZB-06P) should be sufficient for a small room. The maximum range is approx. 4 meters.
I have already used this myself and have had very good experiences with it. However, I have not yet used any other presence sensor as a comparison.
You should know, that people are also detected through wooden doors. In my case, the roller blinds were also detected as movement when they were closed/opened.
This sensor is supported by the test version of the community SONOFF Zigbee app and the official Sonoff app.
