Going Toe to Toe as a Cleric

[Yorkshire]

I'm still in the early levels as a cleric at level 12. Mobs aren't hitting too hard, there are no double attacks coming my way. I'm wondering how long I can continue to melee mobs as a cleric. At what level does the damage and my lack of mitigation start to become a big problem?

I'm guessing once I hit the 20s my idea of meleeing mobs while throwing spells begins to become more of a problem.