What are my best options for staying in Thailand for 5 months with a tourist visa?

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hopefully the land borders will be open by then

Tourist visa for initial part, then find a language school and start learning. Or do a covid extension if they are still happening after Nov 26th 2021.

Honestly. If you dont plan to come in the next couple of weeks I would wait to making plans. My predication is the Thai government will spend the next 1-3 months figuring-out new visa rules. Additionally, surrounding countries may open their borders, making it easy for you to get a new visa.

As other have said TR is 60+30, after that point if they are still doing covid extensions another 60 would be easy but they always late until the last minute to announce extending the program

If you are over 50 you can get a Non O-A visa which gives you a year on entry.

A tourist visa gives you 60 days on entry and you can extend that one time for a further 30 days. Effectively 90 days.

It depends on your age and situation as to whether an alternative visa is available. If you’re over 50 you can apply for a non O visa based on being over 50 and that would give you 90 days. That could be extended indefinitely (a year at a time) as long as you meet the financial requirements.

Other options include an educational visa or a volunteer visa, but we’d need to know more specifics in order to advise on those.

>But with tourist Visa valid only for 4 month (60+60 days).

No, tourist visas are valid for 3 months (60+ 30 days)

>What would be the best choice for me to stay 5 month?

Sadly, Thailand does not have a "5 month tourist visa". My opinion would be to come to Thailand on a single entry tourist visa, and hope one of the borders reopen that will allow you to purchase another single entry tourist visa.