I would also suggest adding a mirror to the back. Sometimes a single
betta will really respond to having a "flare buddy" - even if it's only
his own reflection.

I agree that bettas are very active fish if they have optimum
conditions (very clean water - meaning lots of water changes! - and
warm = 80 degress F). Mine zoom all around, but the single betta I
have is a lot less "swimmy" than the two males I have in a divided 10
gallon.

HTH,

- Lisa