I need hair advice - long frizzy and thick

I have long-ish hair that is EXTREMELY thick and always frizzy. I don't blow dry it and it has a slight natural wave at times. It looks damaged in this photo, but it's just got quite a few split ends, and this photo isn't the best quality. I hardly ever straighten it,but when I do it still has a sort of ring of frizz over it. My hair routine is pretty basic - just a shampoo and condition - and I always let it air dry. Is there any products or hair styles or just general tips that might make my hair less frizzy? Or even thinner so it's easier to manage? I heard thinning out hair can be damaging, but I'm honestly at a loss of what to do, I really dislike my hair.