Think I can help here, passed through BKK on a SV J ticket in early October. At the transfer desk I was told to go to the Thai airlines lounge, think any should work but believe the E lounge is the most familiar with SV passenger access given its near their gate and is where I went although think D lounge is meant to be better.
Basic/slightly dated lounge but food was decent.
oddly I was turned away from the Air France lounge, didn’t think skyteam rules would allow that?
annoyingly you need a paper invitation to be let in to the Thai lounges which they give you at checkin or the transit desk, issue I had was transit desk only opens roughly 2 hours before departure.