Struggling to find a sensor to detect water depth that suits my purposes
I'd suggest that if you are willing to use a small MCU you could use any of the breakouts using the ST VL6180 TOF sensor. Very cheap at around $3-4.
It uses an I2C interface and can measure from 10mm out to around 150mm. The Laser of course will penetrate water ....but you could float a target on the surface to provide a good reflector.