User blog comment:The Heir of Isildur/Best Mage Gear in Oblivion?/@comment-1600847-20130402132353

Whenever I make a Mage, I want him to have as much Magicka as possible. My advice, since you're level 20, is to go into an Oblivion Gate (provided you haven't already finished the Main Quest), go to the Sigil Stone and save your game just as you reach the top. Take the Sigil Stone and check to see if it's one of "Fortify Magicka 50 Points of Self". If not, re-load the save you made just a few feet away from the Sigil Stone and take it again. It will be a different type every time. Once you have the Magicka Sigil Stone, use the item duplication glitch to make eight. If you enchant every piece of armor, two rings and a necklace, you will increase your character's magicka by 400 points.

If not, you can use this technique to obtain whatever Sigil Stone type you want. Since you're level 20, you will get Transcendent Stones, the most powerful type.

As for light armours, Amber or Glass are the best ones. Swords? Umbra or Goldbrand, they're the most powerful swords in the game.