Remington 870 Youth in 20 ga. Not too short for large folks, size and recoil easily handled by smaller statured folks, and even 7/8oz of shot is going to seriously mess up a bad guy's day.
Even with an improved choke, pattern spread is going to be less than 1' diameter at distances you would find inside most homes.
Ed
I've got a NIB Mossberg 500 bantam youth 20 ga. I'd sell if a fella likes this line of thinking.