Make the shotgun an 18 inch barrel model. If it is an auto or pump make sure you get the extended mag.
Although a side by side double only has two immediate shots, it is around 3 inches shorter than a pump or auto with the same length barrel making it a bit handier to use inside.
The intimidation factor would have to be very high looking at those big holes in the barrel.
Check out the Stoeger “Double Defense” 12 bore. Double barrels, Picatinny rails on top (for a red dot) and on bottom (for a light) with a single trigger, tang-mounted safety, 20” ported barrels, green fiber optic sight, and internal hammers. Somebody REALLY knew what they were doing when they designed this one!