Alright I managed to create the behaviour I wanted, I just had to create my own input events, as Flash7 said.
For everyone who doesn’t know how to do that here you go:
(note this was done on a fresh DefaultPawn)
Step 1:
Create the Axis you want in the Project settings.
Step 2:
In your PLAYER CONTROLLER (not the player asset) create the input event behaviour for movement and Rotation.
Step 3:
Finally, in the same Blueprint, also create the behaviour for switching between default and free camera.
Thanks Flash7 for pointing me to the best solution 