Given that anyone can be outflanked, I'd be inclined toward the police style vest with protection front and back.
Most of these will be SPA (Six Point Attachment) vests. There will be two Velcro straps on each side and one over each shoulder. I'd recommend setting up the vest closed and adjusted on your gun hand side (i.e., the right side if you're right-handed), and open on the other side. This allows you to cover the bedroom door one-handed with your handgun and use your support hand to slide the vest on (just thrust the gun through the arm-hole area) and then close the three remaining straps. This can be done in a very few seconds, and at no time does the vest go over your head and obscure your danger scan, or block your use of the handgun.
Spare mag pouches can be attached to the closed straps, and a small flashlight left in the chest trauma shield pocket, which also can accept a cell phone. Set up this way, you've got gun, body armor, spare ammo, spare illumination, and communication device on your person in a very few seconds.