Definitely get a couple of longer one's - at least 350mm, the Buzzetti's are good. You'll find it a lot easier having a bit of leverage. It will also take a bit of time to learn the technique - I can do mine quite quickly now but the first time I changed one it took me hours and I nearly gave up. Best tip is to make sure the tyre is sitting low down in the wheel well (use your knee) at the opposite side of where your working on the tyre.