The single entry non imm O will only give you 90 days, you'll need multiple entry non imm O to leave and return to get a further 90 days or another single entry. You can extend your single entry for 60 days or one year in Country but you'll then need a re-entry permit to leave and return on the same extention.
Many Imm Offices only give the 60 days if you're visiting Thai dependent relatives. Ubon, Sisaket and Jomtiem dont give 30 days and then 60 days, it's one or the other.
You can arrive visa exempt but it's far easier for you to arrive with the Non Imm O(obtained in Spain). It'll save you needing onward travel within 30 days and it should make the process of opening a bank account in Thailand much easier. It will also save you time and money.