a very often misunderstood element the validity of the visa in other words how long you have to actually activate the visa so the OP thinks incorrectly he's got a 90 day tourist visa ( no such thing) he's got 60 days tourist visa but he has to use the visa within 90 days
so if you think going to an IO is less convenient than submitting a non O application I'm baffled as you don't even have to post your passport anymore from many countries I had mine in less than 2 days
If he's married to a Thai lady he can get 90 days on a single entry Non O for £60 which works out cheaper and more convenient than a TR60 and 1 extension which would cost £30 plus 1,900 ( £45 )
why don't you just apply for the evisa then you don't need to worry about going to an immigration office and it's actually cheaper GBP 30 for 60 days a 30 days extension costs GBP 45