Mitsui's Cabin on the Ship
In Japan, rooms are measured in tatami (a rectangular mat measuring 3'x6'). So, if someone has a 6-tatami room, their room is generally 9'x12'. Mitsui has an 18'x21' or 21-tatami cabin on the ship.
Sung has owned several ships in his time as a warlord but, once they served their purpose, he sold them--usually at a substantial profit. He considered hiring a ship for this trip, but none of the ones he looked at suited his purposes. They had all either been used to transport animals, produce or slaves--all of which left the vessels in various states of disrepair and permeated with various intolerable stenches.
When he finally found a ship that was in reasonable repair and had only been used as a treasure ship, he purchased it outright. Even so, he had extensive work done on it. He basically had the entire ship refitted around Mitsui's cabin. Hers was the largest space on the ship and the most lavishly appointed. Spartan and utilitarian by comparison, the crew's quarters were two common areas with 25 bunks to a cabin.
The Captain, Mitsui's bodyguard for this journey, fared little better, only being assigned a small 3-tatami cabin, but at least he had it to himself. Ever the loyal soldier, he decided to sleep outside Mitsui's cabin in order to keep a better eye on her. Even so, in the end, Mitsui had a better suggestion in regards to his sleeping arrangements and her protection.
In a land where space is at a premium and vast areas are only reserved for the very wealthy, Mitsui is traveling to China as a queen.