Let me start by saying I am a MELEE player and I think spell caster's need a buff.
It starts with balancing the abilities.There is NO reason why a player should be 100% immune to fire and magic damage. Currently that is easily doable with a PERMANENT buff called "Protection from Fire". This needs to be a duration like 10 seconds. A player should have to use it skillfully during combat when expecting a fire spell.
Mage armor should NOT be able to be used in anything above light armor. This gives too much spell resistance to melee players and can easily be stacked with their armor for 100% magic resist. Players have been doing this.