I was told by my legal team that if I went to the airport and told them I would have a 2 day overstay they would fine me without consequence. As it happens I had to go to Malaysia so got the 60 day extension. I was in process of getting retirement visa and I took my docs with me but were not required at BKK
thanks to all for your answers, I normally use wise but looked at Revolut and they have a maximum fee quoted as £5 but I have not tried yet. Also depends on currency rate between the outlets. I will feed back once I have tested all 3. But good to know I am not missing anything