Just an update on this thread. On a recent search I noticed that there are now
two 5-star Top Secret hotels (at least) on lastminute.com for Bangkok. I think the cheaper one ($70-ish) is still likely to be Anantara Sathorn (but I can't be sure). The second one - at something like $120-ish a night - is in Silom, but I can't narrow it down any further. It could be a number of places.
If anyone happens to book and confirm, could you post on this thread to help anyone else looking. Thanks