Casting rate is what you would need.
I know always going for more mana potion can be annoying at time so try getting into runeword and crafting.

Here is what you could use.

Caster Armor, magic light, mage or archon plate + jewel + tal + P. amethyst.

The preset mods are:
Regenerate Mana 4-12%
+10-20 Mana
+1-3 Mana Per Kill(<--this is mostly what will help you)

Caster Glove. magica leather gloves, demonhide gloves or bramble mitts + jewel + ort + P. amethyst.

The preset mods are:
+4-10% Faster Mana Regen
+10-20 Mana
+1-3 Mana Per Kill(<--- again this will be what will help most)

Lore (Runeword )
OrtSol in 2 socket helm

+1 to all skill levels
+2 Mana per Kill(<---)
Lowers Damage by 7
30% Lightning Resistance
+10 Energy
+2 Light Radius

Steel(runeword)
TirEl

+20% Enhanced Damage
+3 Minimum Damage
+3 Maximum Damage
+50 Attack Rating
50% Chance of Open Wounds
+1 light radius
+2 mana per kill(<---)
25% Increased Attack Speed

so with that you get up to 10 mana per kill which is something very helpful.