You can use an agent to convert exemption to O visa but they strongly recommend get the O visa outside Thailand. It's possible but not easy.

Michael David Nope

Alexander DThornerian Makes no difference, dividendes are not taxable in Thailand

I went to the office near regional land, they sent me away and not interested

Marcel Sawyer No issue, i did get stopped before and pointed out my long term visa which allows 1 way flights. no problem.

O - A sorry my mistake, O-A is multi entry

Few options as already posted.

Non O 90 day and get the retirement extension

Non O multi entry 1 yr 90 day per entry

Multi entry tourist visa as explained already

Personally i would do O visa and get your 1 year extension which allows a local bank account and renew it with an agent each year, 7k if you have the cash in the bank 16k if you don't.