I'm not sure, but immigration offices have lots of discretion and they exercise it. And things are changing. Years ago, I 'floated around', didn't enter into any long-term (e.g. six months, one year) rental arrangements. Just as long as the places I was staying at had reported my presence--and these were hotels and inns--that was good enough. Now some folks report here they are being asked to show longer-term rental leases. I think it's just a matter what the IO asks for. Since you mention you're likely going to deal with Jomtien perhaps someone there in Pattaya can chime in. Given the abundance of rooms there, and the ease of 'floating around' there I would be inclined to guess the immigration office wouldn't be forcing one to show a long-term lease on a place. But who knows?
