That’s basically correct. You can extend it at an immigration office. Most cities have one. It costs 1900 baht per person to extend.
The ‘border bounce’ allows you to do it all again. It is always at the discretion of the immigration officer but usually it isn’t denied. However, they do have the right to do so. There may also be a limit to the number of days you can stay in Thailand in this type of entry. 180 days rings a bell.
It does depend on your nationality, though. Not all countries are included in this.