I use a pair of JT slide shorts - they have a thick foam pad where it matters. I've taken shots to it from close range, with only minor discomfort
I also play cricket, and tried a cricket box, but they tend not to stay put with all the contortions in paintball, especially sup'air. And if a solid plastic box slips out of place, you can suffer more damage than not wearing one, as the solid walls focus the impact...