To the OP: Sound 357-164.3 Db,9mm 159.8 Db, 12 ga 161.50 18" barrel, no you will not go deaf from firing one or the other, I have and I am not deaf, YET.
Birdshot: I am not sure what size your talking about , but 4,5,6 shot form a 12 or 20 ga at 30 ft or less will provide instant stops with a center chest. I am not aware of any research that shows a "heavy leather jacket" will stop "birdshot", I would love to see the "research". My experience is in the ER and autopsy table, 4-6" ragged hole without heart and lungs proved fatal, immediately. That said I use a semi 12 with 00 buck, I have no penetration anxiety, ( I could 7.62 steel core and not hit anyone). I do not believe there is any benefit in the universal pump sound when someone is at my bedroom door, since at that point they broken into the house, have killed both of my Rotts and are not there for breakfast. 9/40/45 with effective bullets, with good shot placement will all work assuming you have enough light to see, night sights a must. My edc is a sigma 40 f, I own SD40, MP40,glock 22,23,27, plus a few 357 sigs to round that out.there is a 15 rd mag and one in the chamber, a spare next to the light and gun, 2 more mags in the open drawer. Hanging on the wall is a ranger belt ready to go with another loaded sigma and 2 mags,knife, cuffs, etc. Next to the belt is an AR in 300 blk with a can, these are mine, my wife has her own weapons on her side. Last timed response from local sheriffs office was 45 min to shots fired call and they were 8 miles closer, big county , few deputies, not their fault.
Unless you use a suppressor all will be loud. If you want another gun by another spare of your edc or spend the money on ammo, training, and lights.
As stated above this is serious, life changing, treat you tools well, make sure they work, train hard, you are fighting for your life. Do not forget MURPHY!! Be Safe,