I don't have a side-by-side, and the offerings from Stoeger wouldn't be that much more than a new barrel for the 870
If you are really worried about shooting through the walls, load the 1st shot with rubber buck which you can buy here in Ca, it is non-lethal and will cause the intruder to not attempt intruding again, and back the rubber buck with real buck if you need to put him to sleep.
I'm with you I would have a very hard time justifying its use. You should only be firing your gun if you're in fear for your life, if you're in fear for your life you probably want to stop your attacker as quickly as possible and that means something other than rubber shot.Rubber shot is less-lethal not non-lethal. It can and has killed people. More importantly from a legal standpoint, it will most likely be viewed as a use of deadly force, even though it is much inferior in terms of physiologically stopping an assailant.
Some of the best advice in the thread.If you're familiar with shotguns already a shogun would make sense. A shorter barrel for something you have would be the easiest.