exactly right. You can apply for Non O with 30 days or less (some offices allow 45 I believe) but not less than 15 and same for 1 year extension of 3 month Non O
There is only single TR60, no multiple since border runs are not possible. You can arrive with TR60 and then extend for 30 and either hope for a COVID extension being available or convert to a Non O if you have a Thai spouse or child or are 50 and over or an Education visa