Every time I went to Bangkok, I liked to stay in the Davis Hotel as it's very neat inside and very convenient to go around.... especially for those Spas, MRT / BTS, Emporium are very close by.
And there are quite a large amount of Japanese lived in that area, so you will even find quite a few Japanese Restaurant there.
The picture above was the room I stayed at the first time in The Davis Hotel, they upgraded me to the 2nd bottom rank room which also included a kitchen, dinning room, a living room for watching TV / Reading Magazines, a big room with the bed shown in the picture, and a working desk, plus a very big and nice bathroom.
Breakfast included and pricing is very reasonable at around Bhat2,000 at that time. (Not sure how much it is now...)
As I remember, the Japanese Group V6 were staying on the same floor at that time so I got to see a lot of Fans waiting for them down in the lobby. :-P