Maybe get some training. Attend the NRA classes. You will get some real hands on ideas and personal coaching from folks that really know what they are talking about. A gun and cartridge are just tools. Learn to use the tools correctly and a lot of the apprehension about using the tool will go away.
This is what I use at home. Neighbors are very close.
Mag Safe Ammo - Pre-Fragmented Saftey Ammunition Handcrafted In The USA
Different than my carry stuff. Hornady Critical
But if TSHTF I'll shoot what I have....
Wow you're probably going to get as many opinions as there are people here. What do you want the back up to do? Are you looking for pocket carry? My first thought would be the xd-s already in the cal you have and reasonably small. I know some folks pocket carry it. After that maybe the Kahr...
Well not to be too cynical with a nice gesture, but Law Enforcement is probably their biggest customer. From a marketing point it makes good sense to keep their name in front of their best customers.
Finding a Shield may be a bit of a problem check out the tread on one guys search. https://www.indianagunowners.com/forums/handguns/236330-still_shieldless.html