it would have to be a blunt weapon, but even that still has a chance of chopping limbs off.

Making it blunt would also induce a huge strength requirement for using the weapon, unless you stuck with a low quality one.

I think there is a blunt katana in Ultimate Weapons Pack.

You can always first aid enemies, but if they are hurt bad enough it is not always enough to save them. However if they are knocked out and you put a prosthetic on them from their inventory, even a hiver leg, it will save them.

There is also a Mender's mod which makes things easier, it spawns NPCs that run around being free medics to everyone, and also have camps and merchants. You could RP as from their faction.

Another option is Martial Arts or blunt weapons.

Maybe train assassination too, since it is actually a stealth knockout and not killing. There's a mod for training dummies for it also, for lower risk skill leveling.