BJT or MOSFET switch for led indicator problem
It looks like you want an LED to light up when a load is connected, without affecting the voltage to the 1.8K load. The BJT is better than most any MOSFET in this application and yes, the Vbe junction will drop 600mV or more with 5mA flowing. Most MOSFETs need more than 600mV to turn on so even if you put a low value resistor in series with the load you will need to drop more voltage. 

It would be easier and at least as efficient to just connect the LED and series resistor across the load, but maybe that is not convenient for some reason. 

If you want to get to an even low voltage than 600mV it's easier to use a comparator, however the comparator will draw some current from the 9V even if the load is not connected. 

The below circuit will drop 50mV with the load connected. It's possible to go lower again by using a better comparator- this one is very cheap but it has a Vos of almost 10mV worst-case, so I've set -25mV and +25mV roughly as the differential input voltages. It can drive a few mA to the LED if you need more use a different comparator or add a transistor. 







simulate this circuit &ndash; Schematic created using CircuitLab