^ Kirk's quarters, and the briefing room, served that role perfectly in TOS.
True enough, still McCoy got to have an office, and we once heard of Scotty having one as well.
The sticking point, continuity-wise, is that the producers of Enterprise opted to include a ready room in their sets. With good reason, because it is a sensible narrative device for the captain to have an office right next to the nerve center.
From a "in-universe" point of view, it would have been impossible for Kirk to have had a office on the same deck as the bridge. While there a degree of disagreement as to the exact layout of a Connie's top deck, most would agree that there is simply no room for a office in the area surrounding the bridge.