You might look at the short length of pull Hogue stock
. It's popular for defensive shotguns.
As for ammo, conventional wisdom is that large buckshot (00 or #1) is most effective as stopping an intruder/assailant. But people who worry about pellets over-penetrating or stray pellets carrying too far might choose smaller #4 buckshot or or even birdshot. I personally would not use birdshot for defense ammo, but that's one opinion.