Chances of getting a middle seat with one ticket?

Sorry if this question has been answered before, but I couldn't find it elsewhere in the subreddit. I'll be booking my first Spirit flight soon, and was wondering what my chances were of getting stuck with a middle seat as someone traveling in a party of one. For context, flights are to/from Orlando on a Friday and Sunday so I anticipate them being decently full, but it's not during peak travel season so I have some hope.

Additionally, if I want to avoid a middle seat, when do you think would be the best time for me to check in?