.. back to the OP. I have had similar experience in touristy areas in the south. I spend most of my time in Chiang Mai non-tourist areas where native speakers understand my spoken Thai. I don't know how good or bad it sounds to them, but I get by. Last time i went to Krabi and Samui tourist area hotels, i just spoke English. it was easier. I think the trick like others have mentioned is to sneak a phrase in that makes the listener "click" and catch on that they should interpret your words as Thai instead of English.
I have been on the other side too. After international travel opened following a few years of COVID, I flew into Chicago airport after being mostly in Thailand for 5 years. I sat there eating a disappointing burger watching people of all ethnicities walking past and speaking so many languages, including various dialects of English. It was quite a mental readjustment to hear all those voices and try to tune my brain to listen for a specific language.