For our first two cruises, we chose Deck 2 cove balconies (Breeze and Vista) about 8-10 cabins aft of the forward elevators, partly for this reason. Not fully amidships, but enough to minimize motion. We noticed very little motion when in our cabin. However, these were also Caribbean summer cruises with not all that much wave action either (but a couple days were rolling a bit).
Low and center is your best bet. Having sight of a horizon helps - your brain starts to recognize it indeed is the floor that's moving. If you're inside, your brain does not like the fact that your eyes are telling you all is stable, but your inner ear says things are moving. That dissonance makes you want to puke.