@Jurgen *******
, You can apply for a 1-year extension on Non-OA entry. For that, you need to meet the requirements including financial proof and insurance.
You go to the local immigration office at the end of the current stamp to apply for a 1-year extension, then apply for a multiple (or single) re-entry permit to travel abroad during your stamp.
So, you need to apply for an extension AND a re-entry permit to stay. Also, need to do 90 days report if you are staying in Thailand for 90 consecutive days.
METV is an abbreviation of Multiple Entry Tourist Visa, not re-entry permit BTW.