Dynamic Range Current Measurement
With the high resolution you're hoping for, I'd recommend you rethink your high-side sensing approach. What you need to realize is that your power supply circuit ground does not have to be your output power ground. If you're careful about isolation, you can make a supply which looks like







simulate this circuit &ndash; Schematic created using CircuitLab

And you need to float the supply anyways, since you cannot be certain that the customer will not someday decide to reuse the supply in a floating configuration.

As has been commented, doing high-side current sensing requires careful attention to CMRR issues, not to mention the relatively large level shifts required. With 1 mA resolution (and presumably accuracy), keeping measurements within accuracy specs, particularly at high voltages, will be quite challenging. Low-side sensing is far more forgiving.