The splitter that was supplied with your saw is all that you should need. It will be slightly narrower than the blade itself and will rest very close (1/4 inch or so) to the the back of it. If you mount something further than that you can still have problems.

Wood sometimes has internal stresses that will cause it to pinch against the blade or spread away from it after being cut. Either one of these can result in a kickback. A splitter will help greatly to avoid kickback and should always be used.
Mike Boren