I will start off with: Welcome to CF!

Warrior is the most popular class in the game too so you are
not alone and most melee classes play similarly.  So classes
like Rangers and Assassins are going to be more similar to a
warrior.  Thieves are a little bit less of a straight up melee
class depending on how you play it.  

To answer your question, I think any mage class you can learn
with.  Shapeshifter is the closest to warrior.  Each class
plays slightly differently too.  The issue with mages is that
they do not have very much HP.  Between magic and HP gear you
can fill the gap though it might take a while to get up the
in-game knowledge.

If I were you, I would either dive into a class that you want
to learn/RP and stick with it until the end (that is how you
learn the most).  Or play a class you are more familiar with
but is slightly different like an Assassin and start learning
more about mages by helping them out with things.  (I learned
to play with an assassin.)