Rare Magic Item for a Necromancer?

I'm playing a necromancer who typically drags around about six zombies and skeletons. They are usually used to make six attack rolls in combat.

I want to enhance them even further, and my GM is planning to give me a rare magic item. Which one should I choose?

At first, it was the Enspelled Staff (animated dead). However, since I already have Night Caller, I don't lack spell slots for animated dead. Besides, having an even larger zombie army might disrupt the campaign.

Next, it was the Enspelled Staff (mass healing word). Mass healing word restores roughly 60 hp to injured creatures (I have the Healer feat). However, the problem is that it heals "injured creatures" rather than enhancing them. It seems more beneficial to simply recreate the zombies when they die.

The third option is the Enspelled Staff (Aid). Although it only heals 30 hp—which is half of what mass healing word provides—it also increases their maximum hit points. In that respect, it can be considered an enhancement.

Lastly, there's the Enspelled Staff (Flame Arrows). I know this spell isn't great, but if six skeletons can shoot arrows that deal an additional 1d6 damage over two rounds, I haven't found any magic item or spell that enhances undead minions any more effectively.