Choose Breton for 25% magic resistance, or Dunmer for 50% fire resistance. Get the Magic Resistance Alteration perk at 3rd level for another 30%. Get the Lord Stone and the Agent of Mara perk by doing the quest in Riften. That gets you to the 85% magic resistance cap. Good luck fucking atronachs.
Alternatively, you can get over 100% spell absorption with the Atronach stone and perk, and wearing Miraak’s armor. Or be extra sneaky and take the Necromage Restoration perk and becoming a vampire, thus making those effects 25% stronger. Note that having 100% spell absorption means you can’t cast beneficial spell effects on yourself or summon atronachs which defeats the point