A simple option is to apply for a six months multiple-entry tourist visa, but that requires you to leave Thailand once and do a border bounce for a
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months stay.
You could also apply for a Non O and then an extension if you hold a pension and meet the income requirement. However, as I understand it, the Swedish embassy may soon no longer issue income affidavits, in which case you would need to meet the requirement through funds held in a Thai bank account.
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