Your passport.. Officially you need also a return ticket or ticket out of Thailand before the 60 days and the equivalent of 20k in cash... Though highly unlikely to be asked for those
But the amazing thing is you waiting so near departure to sort this out?
friendly tip.. Shoyld be asking any visa information in the future, please include your passport country... You may have received 'friendly advice' but without that information to be fair.. it could be totally wrong advice...