@Laurence *****
You can always apply for another visa. That doesn't mean it will be approved.
If they see you've just spent 9 continuous months in Thailand, they may be hesitant to issue another tourist visa, whether it's single entry or multiple entry. They might happily issue it, they might ask you lots of questions, or they might reject. No real way to know.
You might also get questioned when you enter the country on a fresh visa after spending 9 months as well.