A Rem 870 loaded with bird shot is sufficient
If you check the pattern on your shotgun, you may find that bird shot spreads very rapidly compared to buckshot, at least that's what mine does (the aforementioned 12-gauge 870 Wingmaster with 18.5" barrel). I'm not comfortable that a through-the-kitchen-and-across-the-family-room round of birdshot would be sufficient to end a threat quickly, especially through heavy clothing.
#7 Birdshot at 20 feet -
00 Buckshot at 20 feet (2 rounds, COM and shoulder). Ignore the circled holes -