Differential amplifier input voltage higher than the supply voltage
The differential amp you plan to use has a CMRR that depends on resistor matching, which implies precision resistors. You can buy precision matched resistor networks but that will be expensive. It is simpler to get a canned current sense amp which has everything you need inside. There are tons of options depending on common mode voltage, offset, bandwidth, whether you want it bidirectional (both current polarities) or not, etc. Here's INA180, which costs about 40c in singles at Mouser. It does not require a negative supply.

This one is bidirectional, it has an extra REF pin so you can set the output voltage that corresponds to 0V on the sense resistor... it's also zero drift if you like low offset

...and this one uses a different structure where the voltage to be measured is turned into a current then back into a voltage. This setup is interesting because its CMRR does not depend on resistor matching, but it only works if the voltage you want to measure has a very low source impedance, which is the case here.