To get a triple Perfect+ you must complete each level three times, once on each difficulty.
To change difficulty press L1 when on the level select screen in a world.
Each time you have to collect every single gold and red cross and hit the bullseye at the end of the level. Dying does not affect this trophy however, so feel free to slaughter your character over and over if need be.
So to sum it up - Run through on easy, hit bullseye, run through on medium, hit bullseye; run through on hard, hit bullseye. Rinse and repeat for each level.