This floorplan of one of the homes in the Royal Crescent obviously reflects modern living arrangement, but I think it still is fairly illustrative of the original Regency design. At Number 1 Royal Crescent (now a museum), the first floor contains the dining room and study, with the kitchen in the basement, which was undoubtedly the original arrangement. Georgians liked to have their kitchens at a remove, which is obviously difficult in what is essentially a narrow, vertical apartment home. This Lucy Worsley video shows the lengths to which they kept the kitchen at a distance.
This modern floorplan also shows a withdrawing room and a drawing room on the first floor, whereas Number 1 has a drawing room and a bedroom. Perhaps the biggest change here is the disappearance of the servants’ stairs in the back of the home. Here I believe the space has been used for a study, a bathroom and a dressing room on the first, second and third floors. The floorplan does show a warren of bedrooms on the third floor, and I wonder whether the original Regency floorplan might have been further subdivided.
And as previously mentioned, the second biggest difference would be the kitchen in the basement. Presumably maids would sleep in the basement so they might be able to tend the fires first thing in the morning. In My Particular Friend, I find it difficult to place the inhabitants and have resorted in my mind to imagine No. 3 to be like the TARDIS, bigger on the inside.