The Rembrandt is fine, reasonably priced for Bangkok. It's a bit of a walk to the Skytrain, 12-15 minutes, although a Tuk Tuk would do it in 2. Oddly, it has the best Mexican restraurant in town.
And I stayed at the Katathani a few years ago. We were in the wing over the road and I think we had it to ourselves.
Beach good, with a great Swiss restaurant but otherwise not much to eat in outside of the hotel, and not many shops or things. There was a wonderful boutique hotel and restaurant at the top of the hill called Boathouse which was fantastic and well worth a visit...very pricy though.