I want to include to my design an 'variable offset adjustment' circuit using an operational amplifier. This circuit would allow me to ajust the offset of my design. In my circuit, I already has a buffer (non-inverting unity-gain, voltage follower) in my input, so, I think maybe I can use this op-amp with a potentiometer to ajust the voltage offset level. The thing is that I have heard about this 'variable offset adjustment' circuits, but I don't have any idea of how they look. If I look it on the internet I just found op-amp in which both inputs are connected to GND and that does not make sense to me (and would be against my idea of using the existing buffer). How can I do this? I don't think if it is better to do it in the voltage followers or in the differential amplifier. I don't know if I have this opportunity in the "offnull" pins, the datasheets does not give any clue (maybe this means, that the package has no offset pins?). Would a better solution be to change the part numbers for zero-drift (zero-offset) amplifiers? Would I need offset adjustment in both parts? I need a correction of milivolts.
EDITED: Why this design would not work properly according to an answer to this question?
EDITED 2: In order to understand the discussion and to save a final solution: