I personally make use of the sonoff pow smart plugs, with Tasmota firmware. Though any Tasmota compatible smart plug with power readings will work.
The key thing is that with Tasmota, you can properly calibrate the readings. I have a friend with a high quality power meter. I used that to calibrate my smart plugs, they seem to track within a few % of the expensive one, once calibrated.
Depending on if you have access to an expensive meter or not, this will either be the best bet, or completely useless to you. Your local Hackspace might also be a good option for getting your hands on an expensive meter for an evening.