I wouldn't recommend moving the bridge - its position has a massive effect on the tone of the bass.
Some rockabilly / roots players prefer a high setup, some prefer low, the main thing with slap is getting a set of strings that give you the sound you want at the tension you want - that will make the bass easier to slap, then you can concern yourself with adjusting the string height to suit. Weedwhackers have already been suggested, I know some slappers on here prefer Silver Slaps (Teej and Clarky, IIRC) which feel more like normal strings and don't roll under your finger like weedwhackers do. They are still fairly cheap compared to most bass strings.
I know some adventurous players on here have cut their own bridges to size but it's best to do it from the base of the bridge and that means matching the footprint to the body of your bass - doesn't look like an easy thing to do! Or you could get a luthier to do it for you, which might seem expensive until you compare it to the number of hours you'd waste probably getting it wrong.