It's good to see you have your questions answered! Welcome to the forum!
I would not recommend using Thai Friendly or Craig's List as you won't be able to get a "feel" if an lb would really be up for a 3 some with your wife, even though that may have it listed in their ads. If you go to a bar with your wife, it will be easier to judge if things will work out. As for watching, probably most lbs will be okay with that, but less would be willing to interact with your wife.
I agree with Surin Nix lounge type bars would probably be best place to scout for a willing lb as they are quieter and generally less pressure than go go bars.. In Bangkok there is Check In Bar (which has its own thread) on Sukhumvit between Soi 5/7, and Chaos 9, the former Guess Bar in the Rajah Hotel Complex, just 5 minutes walk from Nana Plaza on Soi 4 (Nana). If you do plan on staying at Lebua, Patpong Road is quite close as well. There are go go 2 bars with significant numbers of ladyboys - King's Corner (which is a mix of about 60% postop lbs/40% ggs) and King's Castle III (which is a mix of about 70% preop/30% postop lbs). It's probably about a 10 minute drive if the traffic isn't too bad.
In Pattaya, there are also a couple of lounge type bars - La Bamba and Lita's, plus a number of LB beer bars, which you can read about in the bars section.