@Paul *********
No, you cannot apply for the 12 month extension from visa exempt. You must first apply for the 90-day non-O visa. Only that can be extended for 12 months. You would need to find out if your immigration office supports converting to non-O inside of Thailand, as not all of them support this. Otherwise you would need to apply for the non-O visa again from a Thai embassy, whether it be in Vietnam or Laos or somewhere else nearby.