I strongly recommend a tourist visa instead. By the way as well tourist visas as exemptions can be extended by 30 days at Chaeng wattana, that reduces the total number of visas in your passport
You could try a land border run to Kanchanaburi. Will give you 30 days plus extension of 30 days. Two such runs permitted per year and this border checkpoint is quite relaxed
Sorry, no experiences in Chiang Mai, but I suggest you ask arond specifically in the forum about practice there. Seems every city is different. For example I heard that for " a special fee " in Pattaya you get 3 instead of 2 months