Fit check/question

How is the fit on this shirt overall? I’m having an issue where the bottom “flap” will sometimes flip up, especially if it’s windy, and show my belly; or if I put my hands in my pockets, it can show a little as well. I’m obviously on the bigger side. I’m concerned if I get a larger size, the shirt will be too big overall. Not really interested in going to a tailor, but I can.