If anyone is interested in DIY and exploring low current standby of the ESP32, I have a number of the boards below you can have at cost + postage.
It can be powered by USB or battery with a choice of regulator. MCP1700 for a total sleep current of 11uA, or the SOIC regulator shown for a sleep current of 38uA. The SOIC regulator will cope with the WiFi switch on pulse.
No USB to serial converter on board, hence the very low sleep current. Program with a standard low cost USB to serial adapter.