Or you can get a mage follower from the College, as some of them are ranged and they can summon atronochs or familiars if you give them the proper staves. Try some followers that prefer ranged attacks such as Fanadel or Aela, as they can distract enemies enough for you to launch a few extra spells, and you'll won't have to worry as much about accidentally killing them. It's really easy to accidentally burn/freeze/fry your follower in the heat of battle when they're surrounded by enemies, and this becomes a bigger problem once you get the higher-level AOE spells. Honestly though, if you're a mage having a tank follower might not be the best in the long run.
She will follow you after you win a fist-fight with her in the Whiterun pub. Plus she comes with steel plate armor, which is decent in the early game and is better than Lydia's default armor. Give her a one-hander and a shield, and she'll be an A-class meat shield. I found that Uthgerd the Unbreakable is a better tank than Lydia.
