How about this:
Because Zombies are walking corpses with no mind of their own and are as likely to shuffle towards the nearest corpse as they are to attack the enemy: Instead of the 'Horde Boss' upgrade; make it 'Zombie Keeper'
One Model in the squad of zombies must be a Zombie Keeper. These specially trained Death Guard Marines are responsible for seeing that the zombies are herded in the direction of the enemy without too many of them wandering astray in the frenzy of battle or getting distracted by a fresh kill. (Even zombies have to eat
WS:4 BS:4 S:4 T:5 W:1 I:4 A:2 LD:9 Sv:3+
Wargear: Plague armor, Bolt Pistol, Chainsword, Frag and Krak Grenades
Special Rules: DeathGuard standard Special Rules, Herd, Immune to Zombie Plague
The Zombie Keeper is responsible for getting his charges into battle. If any unit of Zombies looses their Zombie Keeper, the Zombie Keeper in a squad will round up the stray Zombies and add them to his own.
Any unit of zombies, who has lost their Keeper, that falls back within 24" of the Zombie Keeper of this unit is removed and immediately placed in this unit.
Plague armor is a specially made suit of Power Armor which renders the wearer immune to the effects of Zombie Plague in the event they are struck by one of their charges in the heat of battle.
Plamsa Pistol 15pts
Power Sword 15pts
Power Fist 25pts
Without out a Chaos Codex to refer to, I'm limited to what i can remember about Chaos Marines.
Melta Bombs?! Combi Wepaons?! As other possible upgrades?! I have the memory of a goldfish XD