You have a single entry non O based on retirement.
When you enter Thailand you will receive a 90 day stamp.
If you need to exit and reenter within that period you would require a reentry permit. 1000b
Best to look at the bigger picture moving forward.
To live ongoing in Thailand you need to apply for 12 months extension.
That's actually what you should do this trip.
At very least if you do not have a Thai bank account you could open one with your Non O status.
Note Multi Entry Non O retirement is no longer available.
Edit: @wildoates had another read of your OP.
I notice plan of return to home country to sell up etc.
In hindsight it would have been better for the visit in June ("short stay") to have just come visa exempt entry.
The next time you return you have two options:
1. Obtain new Non O and after arrival be given 90 day stamp and in last 30 days obtain a 12 month extension with funds having been in your Thai bank account for 2 months+
OR
2. Arrive in Thailand visa exempt and apply for Non O (retirement) at local immigration office.
The for 12 months extension same process as outlined in first option #1
Do you currently have a Thai bank account in your name only.