As far as I’m aware there is no need for an international licence as your licence is in English. If you stay 3 months or longer, you’ll need to apply for a Thai licence.
Did you alert the landlord of the couch situation prior? as if not I think some responsibility lays with you for not allowing them to have it repaired before it got worse. Maybe look at getting it repaired/recovered before inspection.
More than likely similar pricing if you were to hurt yourself in Aus without Medicare and insurance. I’ve lived here for 18yrs and needed an emergency operation in Perth while back visiting. Gallbladder removal. By memory it cost me $11,000aud.