Hi Dave & JOdi,
You can always pick up some bonnine at your local drug store before you leave, you may even not need it. These mega ships are so big, you hardly feel the ship moving, so hopefully getting sick will not be a problem. Yes, more middle and lower are good, but also having a balcony or a window will help. Although, once you cruise with a balcony, you will always want one. You can also try ginger, I understand thats also good for sea sickness.
Have a wonderful cruise, hopefully without any seasickness :-)