I also use psyllium husks at times, but the best way to get "fluffy" meatballs is to treat them gently. With wet hands pick up enough meat mixture for your meatball, and form it gently into a ball - don't pack it in like a well formed snowball, but gently roll into a ball. Germans/Austrians/Czech etc are famous for their dumplings, which basically means anything rolled into a ball, sweet or savory, and recipes always stress the light hand. Most also include breadcrumbs, but many do not. My new, current, favorite is liver dumplings, great for soup; didn't think it would work at all without bread, but was mistaken.