Yeah they don’t like too many land crossings. The STV extensions are ending soon anyway so you won’t be able to stay longer than your original permitted stay.
The STV extensions are supposed to be ending on 26th November. Alternative option would be to get a 60 day tourist visa and extend 30 days so getting 90 days. Then you could pop into Cambodia and do that process again. Get to see another beautiful country and save yourself the restrictiveness of the STV.
Apply for an extension at immigration office when there. Easy to do and it’s not like it’s really busy at the moment so should be in and out fairly quickly.
A Non O visa is only valid for an initial 3 months, you can then ‘extend’ that visa for a further 12 months based on retirement as long as you meet the financial requirements to qualify. If you don’t have the resources to qualify, then there are agents inside Thailand that can sort it for you. In that case, the easiest route would be to enter on a tourist visa and then find an agent to do everything for you.
If you have the financial requirements then a Non O extension based on retirement. If you don’t have the financial requirements, speak to an agent who will get you through the process.