Sight question about my 320

I have a 320 model pistol grip 5+1 shotgun and it has just the brass bead sight on the barrel.

It also has an empty Picatinny rail above the action/trigger area, but nothing else.

I actually like the bead sight, but tend to shoot a little high due to not being able to get a good view of it, again, due to the empty rail.

What is my best option here as far as a setup that will work better? I don't want a scope, and I am not sure what should be on the rear, as far as sighting is concerned.