New 07 Yaris S need advice on 18's and springs

[OgDogg]

I just bought a Yaris S 07. I'm about to buy some 18x7.5 rims on 215/35 tires. I need to know what to do to drop it. I don't want to drop it much, and my main concern is rubbing as this is my commuter car and my friends and I are heavyweights. I was thinking of going to the dealership to get the trd lowering springs. Do I need the shocks too or will just the springs do? I really want to make sure that it doesn't rub. So I want the strongest springs that won't compress enough for the tires to rub and I'm hoping I don't need the shock absorbers. Give me some advice and let me know what's up. Thanks.