I'm not sure how well you are going to do without a dedicated range sensor, such as the ultrasound sensor used in the PX4FLOW board. My feeling is that the barometer will be insensitive to meaningful changes in altitude indoors (such as in the range of 0m-2m).
In terms of the controller, I would probably start debugging by tuning your altitude hover throttle in the position controller parameters (it is also accessible from the tuning menu in QGroundControl). That parameter determines the thrust applied when the throttle stick is in the center dead-band position.
Best of luck to you