Get a 18.5 or 20inch coach gun or greener...I'd skip the mini shells, and get some Federal low recoil 00 buck, and or slugs...
The best thing about a double for me is its the scaryest thing you could ever have pointed at you... 2nd is to be-able to have 00 in one barrel and slug in the other and beable to choose which to shoot first...I just read a review, Maybe in Bluepress, that said that the Mini shells are a pain to remove once fired...
My friend had a coach gun, he put a sling on it with 25 rounds, that way if he had to grab it fast, he had the rounds on hand...buy a box of the tactical loads and let the wife shoot them in your pump...though I'll be honest, my wife like rifles better and would sooner grab her 94 trapper in 44 mag (16 inch barrel)
Good Luck!