The law is absolutely clear. if you arrive on a visa exemption or visa on arrival, you must have a ticket out of the country before your residence permit expires. There is no requirement for a return ticket, a ticket out of the country by plane or bus is accepted.
If you have international driver license, it's very easy.
Medical certificate, photo, address confirmation from immigration, 320 baht. Only reaction test and color vision check. done in 10 minutes. Good luck. 👍