Just use a n-chan enhancement mode JFET common-drain follower to make a very high impedance low cap(<5pf) active probe tip that you can make using a tiny piece of PCB copper laminate to attach to the end of a scope probe. Only limit: low-voltage circuits, otherwise a coupling capacitor(5pf)/22-meg input resistor G-S would be needed.
You can supply +12 V to the JFET source and set the JFET drain resistor to 50 to 500 ohms to -12V, maybe OC or 22-Meg gate to source pull-down. The gate to source resistor is not needed once the gate is connected to the circuit point of interest.