Try first 6 months in Chiang Mai and 2nd 6 months Hua Hin or PKK, a bit further south. You'll miss the Smokey Season in Chiang Mai, which is approximately February to May, give or take a few weeks.
Or even try 4 different locations at 3 months each.
Also you don't have to wait until 59 days to extend. You can go 30 days before your 60 days expire and do your extension. The 30 day extension will still start after your 60 days finish. So you don't lose any days if you extend early.