I had a major problem with toxic teammates too until i started using eloking.com to hire a professional player to play as my teammate. Like it was the first time I spent money on a Riot game but man it was so worth it.
It's like not only is the professional teammate I usually play with really good skill wise, but he also gives me tips and stuff while we're playing, and is literally NEVER toxic or anything, so that's a huge plus. Plus, it really doesn't cost all that much, so if you feel like the toxicity gets too much for you then I say give it a shot