"petite"...your body your choice, man. If you want to be a fit twink you don't need gear to do that. You can add a little mass and tone-up nicely doing body weight exercises and using light to moderate weights. Keep that diet clean but do not fear big post workout meals full of healthy protein and calories. Get all your daily vitamins, and not in a multi vitamin. Individual vitamins. Daily: 5,000iu's D3, 25mg Zinc, some B12, B6, Calcium, Magnesium, Fish oil...those right there are pretty important and easy to find in individual bottles at the grocery store. Get those if you don't got them already and research more about vitamins. You stated you don't want to get too big so you're not gonna eat too much which means you can slam some protein shakes during the day. I say get the premixed protein drinks in packs at the grocery to slam pre-workout. I say slam pre-workout because you're already "petite" so putting some fuel in the tank before getting your workout in will give that petite body something to burn.