Cabins located on lower decks, closer to amidships will experience 'less' motion than those elsewhere. For your situation, on a ship the size of Ovation of the Sea, a few decks anywhere on the ship are unlikely to be of any practical difference when it comes to movement and sea (motion) sickness. The weather would have to be particularly bad that there'd be much noticeable difference around the ship and, if that's the case, it's going to be way too late for those prone to motion sickness.
Don't overthink this and enjoy the trip.