so in the end, it's a choice between using many items with small troop loss, or not using item with bigger troop loss.
i prefer the later tho.
i reserve my items for attacking high level player, which is harder to fight than an NPC.

so if u want small troops loss, go for the multi-city strategy, and conquer the NPC under 6 minute.
You can do it if u have 4 or more attacking cities (not necessarily your own city. you can ask your friends or alliance member to help).
the camp time is a very handy tools for this..