MUST??
PPL - then take CPL exams (not ATPL) and add instructor rating via course and flight test.
You could then instruct for PPL's - no night, no IMC (rating).
You could not be paid for doing it.
If you want coin of the realm as well as your flying - then CPL or greater with instructor rating.
LASORS, Section H, and JAR FCL 1.335