Just 0-100 based on where the pot is.
One possibility would be is you could replace the existing pot with a "dual" version.
One section would then replace the existing unit and the second would follow the settings but isolated from the welder circuit.
This second unit could then be fed into say an Arduino analog input and the Arduino coded to read this 0-1023 level and map to an output 0-100.
The Arduino could then drive a display of your choice but any with an I2c backpack will keep wire numbers down and the code simpler.
Naturally power would need to be provided so a typical 9v plug pack fed into the RAW input on the Arduino would suffice.
I have no idea if the size of this would meet you requirements as "small" is a relative size.
It might be possible to house the majority of the gear remote and just have the display where you want it.
Biggest hurdle would obviously be the electrical noise suppression required with any added circuitry.