what's wrong with 711 ambiance?? I've got tens if not hundreds of coffees from 711 and never had issues with ambiance. You can take your coffee out, and hang outside the shop kicking off the soi dogs and beggars. You can possibly sit on the one and only (likely broken) blue or red plastic chair that someone has left there, and which possibly will collapse when you sit down on it. While sipping, you can top up your phone and check how much you have put on since last checked.
And if you are off the tourist areas, odds are that the girls behind the counter start giggling 'where you from', and when you answer they have no clue what you said. Good chances to have a date after their workday, possibly leading to anything. Locals come to talk to you or at least show thumbs up.
And you complain about ambiance of genuine cultural experience!
BTW 711 coffee is pretty good, better than in many small coffee shops.