Let me fill out what everyone else has said. When it comes to a meatball's texture and "lightness," there are a few ways for you to assume control. In order of importance, the three most salient are: (1) Touch; (2) Meat grind; and (3) Recipe (including amounts of moisture, fat and fillers).
Even though touch is most important, let's start with the other two since they come first in the process.
You can use any grind from coarse to very fine. The coarser the grind, the fluffier the meatball -- to the point where they can barely hold together. The meat can be ground (or pounded) so fine it's paste. That's very difficult to handle without making hockey pucks, but when made with a light touch, it will produce a very springy meatball. A Vietnamese bo-vien is a good example. You can also use meats of different grinds -- for instance some Italian sausage along with "regular" grind hamburger. Again, you run the risk of making your balls to dense by overworking the mix to fully incorporate the fine-ground, sticky sausage.
When it comes to ingredients, there are countless ways to make great meatballs with great texture. That's true even if you restrict the set to "Italian" meatballs. No matter which recipe you use, there's always several you'll like just as much. Still, you notice certain commonalities. You need a sufficient amount of binding filler (dried bread crumbs, fresh bread crumbs, cracker crumbs, bulgur, cooked rice, etc.) to hold the meat's fat and moisture as it's released during the cooking process; and you need enough additional moisture to help form a uniform mixture with a minimum amount of handling. Egg is not something you see all the time, but the extra protein can be helpful in holding a loosely packed packed ball together during the initial browning.
Most of us, when we choose recipes to try, mentally taste them as we read. I'm sure you do and that's a good thing. Don't be afraid to try anything that looks interesting. Once you've got the feeling for the texture, you can be successful with a huge range of others' and your own improvised and perfected recipes. Hold on to this: Cooking is fun.
Okay. Here it comes. Touch:
With meatballs you want a very well, but not over-mixed product. How to tell? How to do? In home quantities the easiest way to mix is to mix bare handed.
First, wash your hands very well (duh!). Break up the meat(s), as much as possible into a mixing bowl. Wash and dry your hands, then add the remaining ingredients to the bowl. Let the faucet run during the entire mixing and forming periods.
Wet one hand, and make a blade shape, by extending your fingers straight out from the palm or by curving them slightly to conform to the shape of the mixing bowl. Use your hand as a paddle to stir the ingredites, and combine them as thoroughly as possible without squeezing or kneading. Use stirring, folding, or any other motions which strike your fancy. Improvise. In essence, you're in the prep stage of maing mudpies, so enjoy yourself.
When the ingredients are combined, wash your hands with soap or dish liquid, being careful to get all the fat off, and check the mixture. if you're using a mixture of meats, are they as well combined as you'd like? If not, wet your hands again, break up any offending chunks and mix a little bit more.
By now you've noticed that I've asked you to wet your hands everytime you handle the meat. That's always good technique with ground meat. Remember it for next time you make hamburger patties.
Wash your hands again, removing any fat which stuck them. The fat is a telltale of how well worked the meat is. The stickier it is, the more likely that the meat is over-worked. You'll get more fat on your hands from meat with more fat in it -- so that's a mental adjustment you have to make when you're making your diagnosis.
Of course you can use a spatula or spoon to mix, or even the paddle in a stand-mixer (at slow) -- but you don't get the sensorial feedback which comes from touch. I suggest hand mixing at least once. If you can't stand it, you can always switch to a spoon next time. Food processors work the meat so quickly and transfer so much heat to it (brings out the fat, not a good thing), they're really not the best choice for most applications.
When you've got the meat fully mixed, it's time to form your balls. Using very wet hands, roll them between your palms as gently as possible. Depending on the mixture and the cooking method you can make them any size you like. Just remember to use a soft touch. If you know how, a nice altertnative is using two spoons to form quenelles.
My favorite meatballs are made with beef, pork and veal; or, beef, pork and lamb; or, beef and raw sausage; or chicken dark meat; or ... well, you name it. My favorite is all of 'em. If not using sausage, I mix about twice the amount of beef to the combined total of the other meats. Sausage brings so much flavor and incorporation problems to the party, I use at least three times as much beef. The ratio of 1 cup of filler/binder per pound of meat is not bad at all; but I dance around it. By the way, fresh crumbs make for a fluffier ball than do dried. At some point down the line, try rice (porcupine meatballs) and bulgur as fillers. They're both wonderful.
Oh... and don't forget about koofta, luleh, and ... what a brave new world to have such meatballs in it.