What is the best visa option for a pensioner planning to stay in Chiang Mai for 3 months?

correct, brits get in for two weeks without a visa

You don't need to do a visa run. Get a Single Entry Tourist Visa at the embassy in England. That will get you a 60 entry stamp. Then, before the 60 days is up, you can go to the local immigration office in Chiang Mai, pay 1900 baht and get a 30 day extension.

If you think you'll be staying longer or travelling to other countries, get the Multi-Entry Tourist Visa which lasts for 6 months and every time you come into Thailand you get a 60 day stamp (you can extend any of these entries by 30 days at local immigration).

Type O for pensioner

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Have a look at the 12 month Multiple entry O visa available in London for those of 65 and over and drawing a state pension. You simply need evidence of drawing a state pension.

Ian Martin, how old are you if you don't mind me asking?

Garrett Greenwald isn't that what I said ?

@Ian *******

no, its the card they stapled in yr passport. No further extension possible.