Click on the review tab and then select Ventura. In the last two weeks there have been some good reviews on cabin sizes, facilities and positions, particularly the size of balconies and privacy. Over to you. Richard.
Unfortunately I think that you will find that all standard inside and outside cabins are around the same size at about 160sq ft. Depending on where exactly they are on the ship you may find that some of the inside cabins are a little "squarer" than others. A study of the deck plan and a chat with P&O would probably help you to track these down. I don't know what sleeping arrangements you have in mind, but there will be two lower beds in your cabin and an upper bed which folds down from the wall. Once you get things sorted out, I don't think that you will find that you have to disturb your sons sleeping habits too much. Happy cruising.