Im sure the 30 day ext will be no problem. HOWEVER, since the change to 60 days visa exempt immigration are MUCH harder on individual border bouncers (go with a visa bus seems ok). Basically i had the same issue and they made it clear that the 60 days is 60 days (or 90 days) then leave leave not just for a short period. Those need a proper visa and it wont be long before entries start getting denied
. As per advice, never overstay if at all possible. Im here on a 60 day exempt plus 30 day extension then short holiday in malaysia then back on 60 day visa exempt again plus 30 day extension effectively gives 6 months which sounds like thats enough for you. Youll need to book a ticket out within each 60 day period to satisfy immigration but thats about 15 euro for a throw away ticket. Doesnt have to be a flight out, immigration were happy with a ferry ticket