Welcome to the forum Dominic20.
A betta is much like any other bored animal, it lays around and does nothing until you disturb it. As I see it, and this is just my opinion, what he really needs is a companion to get him moving and keep him interested. I keep my betta in my endler tank and he is never sedentary nor is he ever bored for long. The endlers are constantly moving and the betta finds plenty of other fish to interest him with their movements. I have a hard time even getting a picture of my betta because he is always on the move and never lays around sleeping. I am afraid you have fallen into the trap of many people who only keep bettas, the bettas are kept alone and never seem to learn to move around like real fish.