Whatever shotgun you get, reduced recoil 00 buck is pretty cool stuff- significant reduction in recoil, but still truly sufficient penetration and oomph.
Might I also suggest a pistol caliber carbine like a KelTec SUB-2000?
Folds to 16x7" if you like. Light, compact, better range, more precise, and cheaper to feed (and to practice) than the shotgun. Less recoil and blast too. Takes Glock, S&W, Beretta, or SIG mags. .357 mag ballistics at 50 yards.
Might I also suggest a pistol caliber carbine like a KelTec SUB-2000? A guy at my local gun shop was picking one of those up, and said he had been waiting on it (special order) for months. It took Glock mags (I think Glock 19), and I was pretty darned jealous.