Using a SONOFF SV WiFi switch to detect 12V?

Hello together

I am looking for a device to detect a 12V current from a float switch to automate a borehole pump. I have a water tank (no power supply, but wifi reception) and would like to install a float switch which will turn the borehole pump on (both are a few hundred meters apart but in the same network). I thought of a setup with a little solar panel, 12V battery and a Sonoff SV switch which will the detect when the 12V current is on/off. I saw the isolated mode here and think that might work. The Wifi circuit is always up, when the relais circuit is interrupted HA is firing up the pump.
I would like to get some advice before I bolt things together which do not work. I found a similar topic but am not familiar with using an ESP8266 board. It is also more expensive than the SV switch.

Does anyone has an opinion or some experience with a similar case?

Greetings from the farm.