It sounds as though you haven't cruised before! My advice is book a midships balcony cabin as opposed to bow or stern. If the sea becomes moderate or rough then the up/dowm movement is hardly noticable. Be on the rear or front and it can get like a funfare ride.
The F grade cabins at the stern have open balconies and provide a view of both sides of the ship - as such they are worth the extra if you value this vista.