As for your question on prekilled and frozen thawed...Yes, you can buy prekilled mice or rats. If you find a pet store that is fine with it, sometimes they will kill the rodent for you, then you take it home fresh and warm and can safely feed it to your snake. If it cools down a bit on the way there and loses its natural body heat, you can just put it under a heat lamp for a few minutes until it warms up. Having it warm is key for bp’s usually. If it’s cool, they won’t detect it well with their heat pits and may just leave it.
As for frozen thawed, this is the main choice for successful snake keepers. You simply buy already killed and frozen rodents. Or you can buy a bunch of live ones, put them in a bag and give them a good whack on a wall or hard surface to kill them quickly, then freeze them in bags yourself. Then when it’s feeding day, you can take it out of the freezer, and maybe put it in the fridge so it’ll begin to thaw a bit(sorta like when someone takes out frozen steaks and puts them in the fridge all day to thaw a bit before cooking). Then when you’re ready to feed, just get a bowl of hot tap water and put the rodent(still in bag) submerged in the hot water. This will warm up the mouse a bit and make sure the middle isn’t still frozen or cold. Then just pop it under a heat lamp for a minute or two to get the outside temp of the mouse nice and warm and feed it to your snake. Since it’s not live, you may have to take the mouse by some tongs and wiggle it a bit to get the snakes attention. Usually after a bit of wiggling, they’ll attack it thinking its just any old live mouse, lol. I personally like frozen thawed because it’s safer. I dont have to worry about my ball python getting chewed up and killed, the freezing process kills any living bacteria or parasites that may have been in the mouse, it’s cheaper and easier to buy in bulk and stock up a bunch of feeders in a freezer for whenever you need them, and it’s just easier than having to kill the poor thing myself, lol. It sounds like a lot to prepare for a feed, but really it isn’t much. With just those adult mice(that seem small and not so adult at all..lol I was surprised at their actual size), you shouldn’t have to do much to thaw them. They’re so small, just a half hour in some hot water(change the water a few times to keep it hot) and it’s all thawed and warmed up. But with bigger prey like medium adult rats, you’d be better off doing the whole freezer, fridge, hot water, heat lamp process.

Anything I didn’t cover? Let me know.