Kind of depends on your reasons for killing … and whether it’s the actions of killing that bothers you most, or whether you fear you’d never ever want them to die in any manner whatsoever.
There’s euthanasia as others mentioned here. Things happen to living creatures, either internally or they get injured in some way that euthanasia makes the most sense. You might want to have a chat with your veterinarian about humane options that you could do yourself in an emergency. If you can’t even have that kind of a discussion, then maybe this isn’t the right thing for you.
Then there is killing for meat. There is a little bit of technique involved, and certainly it’s not fun or neat and tidy. I can totally get how you might not want to be the one to do that personally. In our area where there is also a lot of deer hunting, there are meat processors that will take your live animal and return the neat & tidy packages to you.
But if you think you’d have a problem conceptually ever letting the critter go, holding it in as high a regard as a dog, cat, or horse, well that’s awesome, and I applaud you for wanting to take that approach, but you’d better have some deep pockets for some length of life and quality of life extending.
I don’t have any chickies yet, but I hope to eventually. Eggs would be my primary interest, but I would not be pouring a lot of money into treating them like household pets. I would be seeking assistance with the meat processing end of things. We have a great farmer’s market here with a lot of egg sellers. I would probably start by reaching out to them to find out how they do their processing, and see if maybe I could hook up with one of them to do my killing for me when needed. Best of all if I could find someone who would teach me what I need to know, and let me decide from there if I could do it on my own.