I am not going to be of much help as, while I have been to many of these places and hotels, it is all quite some time ago and things change. That said, I enjoyed a couple of stays at the Conrad in Bangkok back in the day. If you did want to think about any other properties, I would suggest somewhere on the river as it has a character all of its own, including the various water transport options.

The Fullerton is nice but I think not a member of any of the hotel chains where you have status (I realize you intend to pay cash so that may not be a major issue). It certainly is close to the marina.

Anywhere where you can get an upgrade to a club/executive level room, or at least club/executive lounge access with a regular room, would be worth considering. Or even just pay for the upgrade (e.g., in the Langham Jakarta). In Asia, unlike the US, in addition to free breakfast generally in a special lounge you will frequently get free evening drinks and (often quite good) snacks.