Here's the last hotel I stayed at. It's the CentrePoint on Wireless Road, which is near several embassies, such as those of the US, New Zealand, Netherlands and Japan. Apparently, this is not the Central Business District yet as I mistakenly assumed in the video.
The reasons why I booked this hotel were the wifi (strong and fast the entire time! I found that their malls were not generous with free wifi :-P) and the balcony, which gave me a calming view of the Bangkok skyline, or at least, part of it.
It's less than a 5-minute walk from the Phloen Chit BTS. Room service is even more expensive than S31's, which is a luxury hotel compared to CentrePoint. (S31 also has inexpensive spa services on the ground floor.) I rarely bumped into people except during breakfast hours, so if you want some peace and quiet, then you'll like it here. It's only about one, two stations away from Central World and Siam Center. You may also walk if you have good shoes on :-)