I do the same every winter. 60day tourist visa online. You can do it in bits then submit later- not before 3 months prior to arrival. Then extend when you are there for 30 days more.
You need a hotel booking for some of the time for the visa- it asked you who invited you. I book a return flight within the 60 days then change after arrival but there are other way. Thai airways always check mine. Go and play on the evisa site and start putting together to uploads you need then it will be quick and easy in September when you can do it. Good luck