The use of a load cell for adjustment and help by modifications is already years known (Airtripper , Prusa)

The build is simple

ATmega328 (uno, nano with USB)
HX711 at 80Hz
Load cell for Bowden-setup 10kg and direct drive 20kg

J-head/E3D mount 3mm filament direct drive

The J-head/E3D mount is connected with a piece of M6*26mm (3mm filament V5 thermal break clone) on one side of aluminium bar and on other side two M4 screw holes for the load cell.
From load cell is one M5 thread replaced by a M6 which lines out with the M6 in aluminium bar and provides with another V5 heat break clone the connection with the heat-sink.
(heat-sink, bore 3.2mm, Bowden type for M6 PC4-2 male push-in)

The 1-2mm air gap can be made with washers or cut some material from the aluminium bar

 

1.75 mm filament

Instead 3.2mm hole through, are 1,75mm M6*26mm with liner type heat break used and 2 pieces 3mm OD 2mm ID PTFE tubing from extruder gear to the air-gap and from air-gap to 1.75mm nozzle.

 

Bowden-setup

The hollow M6 which connects the heat-sink to load cell is replaced by a M6 PC4-2 male push-in and the J-head/E3D mount with M6 thread for an M10 to M6 reducer bush

 

 
HX711 library
Simple Arduino sketch for serial monitor readout