You need good OpAmp like OPA335 -
Texas Instruments - and some circuit for transfer current mesure signal from floting shunt to near ground ADC input. May be like that is in INA198. Fnd some cir. for powering floting OPA335.
In circuit floating with shunt we can use optocoupler 4n35 (or faster one - 6n136) for overcurent signal transmition to turnoff MOSFET driver.