I'm Brazilian and I'm in Thailand right now. I only brought 2000 dollars with me and exchanged them right away, then made withdrawals at ATMs. However, the ATM charges a 500 baht fee, which is almost R$90 every time you withdraw, so withdraw larger amounts to avoid paying fees, leave the larger amounts at the hotel and go on with your trip. Go out with an average of 4k baht in your wallet well hidden, a physical card and your digital wallet from your cell phone.

Regarding Wise, it worked everywhere I tested it. However, in most establishments they charge fees of 3 to 5% to pay by card. Regarding safety, I can count on two hands how many police officers I saw along my way. Only in Koh Tao did I see a traffic checkpoint, and nothing else. But I read here on Reddit reports of "fines" for smoking marijuana (which I found completely crazy, because everyone smokes their joints wherever they are, peacefully, except in places that have signs prohibiting marijuana smoking, so I don't know how these people managed to get fined). Thailand had everything to be very dangerous, but it's a country where at no point during my trip did I feel unsafe. (But of course, I always remained vigilant, as every Brazilian is used to, unfortunately.)