Howdy,
If you have the adapter, a Mossberg 12 ga Shockwave can use short 12ga shells. I think great for home defense.
Don't know if anyone is making shorty 20 ga shot shells.

Another gun I am seriously thinking of getting and accessorizing is a Kel Tec CP33. 33 or 50 rounds of 22 lr.
Add a brace, optional 50 rd magazine, red dot optic, Suppressor, flashlight and good to go.
But that's just me.