When we next see him, his cabin is down on Deck 12, then perhaps on Deck 3, and once on Deck 5.
So the answer might be, any Constitution skipper other than Kirk the wandering gypsy had a Ready Room and a Conference Room right next to the Main Bridge (one deck down).
The Gypsy Captain came onto the Bridge,
Up from the planet so shady,
He whistled and he sang 'til the corridors rang,
'Cuz he won the heart of a lady...
Why is it called a "ready" room, anyway? Ready for what?