We all can suffer from analysis paralysis, there are tons of options and all have pros/cons. You can really go down the rabbit hole on this topic. My recommendation is to just pick one and don’t look back 
9mm is definitely an effective caliber, so I don’t want to dissuade you from using it for that reason. I was just pointing out that if the concern was over-penetration, then, you may need to re-evaluate.
9mm Pistol Caliber Carbine (PCC)
- less noise/concussion
- less recoil (faster follow up shots if needed)
- shorter barrel (3-9" are common and viable) (potentially more maneuverable)
- (for you) no new calibers
- Depending on the PCC you get, maybe share mags with your pistols too
- generally more penetration than 5.56, less than 300BO
300BO
- more noise/concussion
- more recoil than 9mm
- slightly longer barrel (8-9" is sweet spot)
- ammo is stupid expensive right now, $1.20/cpr is the low-end. Pre-COVID “cheap” ammo was $0.50/cpr
- more effective
- generally more penetration through barriers (just as heavy as a pistol round, much higher velocity)
5.56/.223
- way more noise/concussion, especially in short pistol barrels 10-12"
- more recoil than 9mm
- even longer barrel (10.3 - 12.5" is sweet spot for pistols)
- ammo is nearly same prices as 9mm
- more effective
- generally less penetration through barriers (way lighter than a pistol round, much higher velocity)
I really like 300BO for home defense because using supersonic rounds its a rifle caliber in a really short package (but not as short as a PCC). I’m not sure it’s more/less loud/concussive than 5.56 in something like an 11.5" barrel without a suppressor.
You can use subsonic rounds for less noise, but without a suppressor IMO that doesn’t have much appeal because you lose so much energy and its still loud. If you didn’t know, there are two sources of noise in a firearm. The “bang” of the explosion in the chamber, which is mostly suppressed by a suppressor. And then the supersonic crack as the bullet breaks the sound barrier leaving your barrel if it’s going fast enough and that is not suppressed by a suppressor. An effective suppressor (read, expensive) can effectively mitigate the “bang” but not the supersonic crack no matter how much money you throw at it. This is another rabbit hole, i’d be happy to expand further if the above doesn’t make sense.
You can suppress any firearm if you have the money, the time (waiting on ATF), and don’t mind putting your name on a gubment list. It’s not exclusive to 300BO.