Easiest semi long term visa for you would be the DTV. Use a thai soft power activity like thai language, muai thai or cooking. You only need to show documents from the school and the equivalent of 500,000 baht in a bank account. The visa is multiple entries for 5 years. Each entry stamp is 180 days and you can leave and come back for a new stamp. This would give you lots of time to figure out your retirement visa while already living in thailand. The visa application fee is only 10,000 baht like $300.