Sonoff Basic without using the relay

I have installed a Sonoff Basic behind a wall switch. I don’t need the relay portion as I only want to know when the switch is toggled, so there’s nothing connected to the output side of the Sonoff. I want to expose the position of the switch as on/off in HA frontend, but don’t know how to configure it in the code. Below is what I have currently. Any help is appreciated. Thanks!

binary_sensor:
  - platform: gpio
    pin:
      number: GPIO14
      mode: INPUT_PULLUP
      inverted: True
    id: relay
    on_state:
      then:
        - switch.toggle: relay1
switch:
  - platform: gpio
    name: "Master Light"
    pin: GPIO12
    id: relay1