Take Battle Caster (Complete Arcane) to get spellcasting in medium armor and wear some mithral full plate.

Take the Goad feat to use your high charisma to draw enemy attacks.

At this point your main issues are lowish HP and fortitude - boosting constitution is one way to fix that (gnomes are +2 con, -2 str, dragonborn gnomes are +4 con -2 str -2 dex) but spells Vampiric Touch can also help. The Bonded Familiar feat can also be useful to turn your familiar into a 1/day damage sponge.

Amulet of Tears from MIC is a nice source of temporary HP with very low cost attached.