I would recommend being a White Mage. They get Healing Hands which heals themselves whenever they heal another, up to half their Spellpower, so getting that the higher the better. Your Willpower will be the stat that affects that, I believe.
Then consider using Healing and Group Healing spells. Those will be a good starting point for keeping your party's hit points up. I think the White Mage will get those automatically... so you're pretty much set when you click on White Mage at the beginning of the game.