If you are in Bangla Road, one often asks whether you want to see a ping pong show. For us that's not what we like, but you first come to Thailand, you probably want to see.
With massage, it is a lucky, if you're doing enough, you make it enough. But I can not tell if you go there then it happened. For one man alone is Soi Kebsub the street where it happened, but there are many more. For a couple is more lucky, and the entrance to the ladies a little fun and a little bit let them know you want a special massage ... then good luck
Hotels are on the internet enough to find, even with all reviews from users. Many hotels are beautiful especially in the 4 and 5 star category. But they often ask a 300 to 500 baht for an extra girl. Sometimes my wife managed to have the lady take it to the room and then I just five minutes later. Apparently they think that my wife and the girl know each other as friend and then she did not dare to speak.
I know of no specific bars where swingers come together. In any case, I never noticed.