A small update for anyone who might find this thread still useful.
I finally managed to convert my Sonoff M5 switch to ESPHome.
More info here.
After flashing ESPHome the M5 now uses ~0.5-0.6W of power continuously when idle. A significant improvement from 1.3W on original firmware. I guess the wifi led contributes to some of it.
I also just tested the Athom switch and it is superior to all others. Installation is trivial, quality is ok, it comes with preconfigured ESPHome firmware, so no flashing required. And the idle power is not measurable, next to 0. The status leds on this device are super-dim when light is off.