If you are leaving and not planning to return i wouldn't worry about it. But if you do plan on returning you could be fined for failing to report if they happen to notice. Worst case scenario is a 2k baht fine
There are a number of different visas all referred to as retirement visas. The Non-O is by far the most common but if you want a Multiple Entry retirement visa out of the box it may also be worth looking at the Non-OA option. The drawback is it requires insurance and a police check
says there are a small number of immigration offices that don't do the in country 90 day Non-O visa for retirement although they will do extensions of stay based on it. It looks like Songkhla is one of those, a search on Facebook shows this happened to at least one other person a couple of years ago. Given your location it's probably easier to pop over to one of the consulates in Malaysia to apply for the visa than anything else
I think now if you want to do your 90 days online then you must submit it in the period from 14 days before the due date to 7 days before the due date. You've still plenty of time to here back though, you can submit in person from 14 days before the due date through until 7 days after the due date.