You could get up to 75 days with visa exemption 45 on entry + 30 extension.
Also look into the covid visa. Think it’s 45 days and able to extend multiple times. I’ve heard this is ending in September and last extension will take you to November. So if you’re travelling soon you can get at least 3.5 months in Thailand.
Conditions say you can’t change a covid visa into any other type of visa. Your only options are to exit the country and enter on a different visa or use an agent. That option is obviously at your own risk as it’s not an official route but yes, overlooked.
Are you looking to stay in Thailand more than 60 days? If you are, entering on a tourist visa won’t avoid questions why you don’t have a return ticket anymore than arriving visa exempt.