Seriously, about the best you can get is the Hornady TAP 00. Sacrifices one pellet for much higher velocity, 1700fps IIRC, and it also has reduced recoil compared to Federal 00 2.75 mags but a little more recoil than the Winchester LE reduced recoil 00. These shells have that same Federal Flite Control Wad that everyone goes on about. And for good reason, these printed a nice desert or salad plate size pattern at 25m with all shot evenly spread over a consistent area using a 16"bbl. I tested probably twenty something different shells, different brands, shot size, etc., and of all of them, these performed the best overall, and 00 is commonly associated as being a manstopper. These shells are also available. Steer clear of mixed shot, shot and slug, etc., none of them ever made a decent pattern. These TAP 00 will make a fist or saucer size pattern at most SD ranges and maintain that perfectly distributed pattern, and that's about perfect, especially when it's hauling ass at 1700fps, that's about 300-400fps faster than most 00.
The next best thing would, some may say the first best thing, would be the reduced recoil slugs. If you like 'em, you can always put 'em in a side saddle to load up if need be. 000 is nice I think, but it always comes in hard recoiling magnum shells. Follow ups are much slower with hard recoiling ammo and some reduced recoil ammo doesn't give much up or even gains, like the TAP 00. With slugs for HD, the reduced recoil are all that's needed given the weight of the slug. .70cal 1oz. hollowpoint rifled slug moving at 960fps is more that sufficient, especially if you can have another on tap in a second or two. Or several 00's moving at 1700fps., take your pick. Just stay away from gimmicks and powerful hunting loads unless you don't give a shit about penetration, your walls and shit, and have no neighbors.
For self defense, you kinda want to try and keep the recoil down the best you can because follow up shots can be critical and sometimes it's better to put two lighter shells on target than one magnum shell. Or what if there's two or more bad guys? IF recoil isn't a problem, the Winchester XX 3" #4 buck with what, 42 pellets per shell? That one is fucking brutal and one square shot with that and it's over. You'll feel it too.
You really can't go wrong with ammo selection for a shotgun, but you do wanna keep it #1 buck or heavier; #4 isn't bad either. That birdshot shit doesn't always work and I wouldn't bet my life on that. Stay away from mixed shot or buck and ball unless it's loaded right, you've tested it and it's consistent and tight. Doubt you'll find that, I didn't. Mine is now like a Shockwave, just a breacher (and I'll probably never breach another door again in my life) so mostly for fucking around I guess. Suppose you could still use it up close.
That said, I use a suppressed .300BLK SBR with 125's. It's perfect. Unless you can have an SBS, I see more limited use with one indoors. A 5.56 SBR is nice too, but you can make it shorter with the .300BLK and not lose much in velocity, especially at HD ranges. But I also use an alarm and have warning time enough to rack the rifle and turn all the shit on. A set of soft armor handy isn't a bad idea either, something you can just pull over your head fast. If you have time.