Chris, . . .
You need: 1) a round that will do the job, 2) one you can carry more or less 24/7, and 3) something subsonic.
The answer to all this is very simply a commander size .45ACP.
The "report" from that particular caliber is less of a sharp "Crack" than it is an extended "Boom". And you can buy lower powered rounds that really take the noise factor down.
It is NOTICEABLY less irritating than either a .38 special or .357, . . . .41 mag, or even .44 special.
"Silencers" are cool, I know a guy who has a couple of em, and I have shot em, . . . they are NOT a CCW type idea.
Long and short, . . . the .45 has also one other thing going for it, . . . the .22 may take a full magazine to do the job, . . . the perceived vision the bg has when he sees the business end of a 1911, . . . may be enough for him to decide he has to go change his refrigerator light or something. If it isn't, . . . one or two at the most rounds in his bod, . . . you will have discouraged him big time, . . . OR, . . . you have a problem needing a battle rifle.
May God bless,
If you can breathe, . . . thank God!
If you can read, . . . thank a teacher!
If you are reading this in English, . . . thank a Veteran!