In the length of your living room, #4 will perform the equal of anything else, but overpenetration will be reduced significantly. (You wouldn't want to destroy your next-door neighbor's wife or favorite spaniel, now would you?)
Why would you want to use OO buckshot inside the house anyway? 9, .36" "pellets" per shot seems much too likely to cause as much damage to the house as to the intruder! #4 Buckshot or maybe even BB would work just as well in an intruder without tearing up the house!