I believe the UK embassy only touts the single entry non-O. However, when you apply online, the drop down list shows multiple entry. I just clicked on that and it worked, no need for any special 'proof' either. Maybe I was just lucky but I'm not knocking it.
No, I believe they are looking for ฿65,000 pm. The state pension alone may not cover it. I included my other 3 pension statements too. A bit strange, as receipt of state pension is a requirement for this visa. Otherwise, you may need to show £10,000 in a bank statement.
I recently obtained a one year, multiple entry, non-O visa based on being over 50 with state pension, from UK. It was surprisingly straightforward to obtain online. Apart from the usual passport copies, photo etc, I uploaded my pension statements and travel insurance covering letter. Approval came through by email in a couple of days.