If you are doing a standard PG cruise you do not cruise much in the week and are parked a lot of the time in a lagoon. Using the ship like a hotel. So I would not worry too much about the sea sickness issue.
738 is midship but there is a vibration that starts at 742 and moves forward and back a few cabins. Not sure why it is there but it is there.
Not a big thing but if you can move a little further forward it might be better
