The incompetence of the AI generally prevents the player from fighting good field battles, as the enemy won't train quality troops and won't organize armies intelligently. You have two basic options, you can use the console to spawn stacks for the AI, or you can play a mod (Like Broken Crescent) which helps the AI out with it's field stacks.

You can also wait for the Mongols and Timurids, as they provide pretty good field battles.

In my experience you can get some okay smallish field battles out of Turkey, Poland, Byzantium, and Hungary in the early game (first 30-40 turns) and by then you're not far from the Mongols. Try playing Venice and going east?