When It's core only I suggest a Druid Cohort.
He can Buff, Heal, and Serve as a mount.
He also bring with him another Warrior to help carry your loot.
Then his Cohort could be a bard, since you will be having quite a few characters.
Alternatively consider a transmuter that focuses on buffing you, it will still feel like you are doing all the work, while it is actually the transmuters spells that are the source of your power. It also gets you easy access to things like flight, haste and identify.
However, when in Core only, the simplest answer is: Go with a druid, you can never go wrong with a druid.