*summoned*
Grrrrr... What is it now mortals?! Who Dare- Oh...
Another novitiate of the Dark Arts whom seeks wisdom from an accomplished Lich of yore? Blessed be my child, I call you brother/sister.
First things first, I[and anyone else with advice] need to know what platform you are on. If you are on PC, then oh boy, I can hook you up with unlimited potential. For now, I'll just assume you are on console.
As other's have already suggested, the Aetherial crown + Ritual stone is one of the best and most effective combos you can utilize for a genuine necromancer play-style in vanilla Skyrim. Basically, you are going to want to use the in-game necromancers as a starting point. Keep an eye out for dead bodies to resurrect. Work on getting the Dead Thrall spell as soon as possible to have permanent resurrect NPCs.[humans, elves, and beastfolk only] For summoning, get to the Soul Cairn in the Dawnguard questline ASAP. You can find three undead summons there.[Boneman, Mistman, and Wrathman]
Also, as a Vampire, you can utilize the fortify resto loop exploit to brew godly fortify conjuration potions. Drink one in conjunction with the Vampire's unique stage 4[highest level] reanimation power to permanently resurrect a Draugr Deathlord. This ONLY works with the Vampire reanimation once-a-day power. A normal Dread zombie spell will not work[the Draugr will disintegrate upon changing locations and cells.] OR, if you are lucky enough to acquire a Dread Zombie staff, you can pull this off[reanimation staffs can reanimate corpses numerous times, they NEVER disintegrate.] I presume you could also craft a Dread Zombie staff with Dragonborn DLC, but I'm not 100% certain.
You could also play a hybrid Dark Artist. I usually don't discriminate, and freely summon daedra and resurrect undead depending on the situation. Being on PC, I usually have a reanimated Draugr boss following me, and then summon an Atronach or Dremora if needed.