yes correct ,yes you can do with tourist visa while in Thailand no agencies only find a school first you must choose the location where you like to stay
I had ED visa and everything was done by my school all I had to do just pop up to immigration to make a photo every time when I had updated my visa the school was in Koh Samui.
You can do tourist visa 2 border run you will have around 7 months and later you can do 2 years education visa and after that you will be nearly 50 years retirement visa. If you can’t do elite visa.