Go for the low truck profile if you want to obtain additional stability when you do flip tricks. It also works well for small wheels. The mid-sized trucks are good for all-around use, especially in streets and parks. You can also choose the high-sized trucks that are good for carving and cruising, which is the reason why they are perfect for huge wheels.
To get higher ollies, I would suggesting resting your back foot on the very end of the tail and the front foot in the middle of the deck to allow for more slide. Popping as hard as you can and catching your board in the groove of the nose with you ankle practically resting in the groove will level the board out in the air. after this initial movement slide you feet back to the bolts on the tail and nose to ensure a clean landing.