Most people think of a "bump ski" as what the pros use to ski zipper lines at high speed, which is something to aspire to, but not what you need at this point. You need a ski that is forgiving (i.e. on the mellower side of the stiffness scale), especially in the tail. Bumps continually try to push you in the back seat, and this it exaggerated by a ski with a stiff front section, and then quickly punished further by a stiff tail that accelerates you when you want it the least. IMO you are looking for a ski with an even (front and back equal) medium soft flex, and a sidecut that is not very deep. A wide tip is OK, but not a real wide tail, which will hang up at the end of the turn.
Good powder skis (soft and straighter sidecut) tend to make good bump skis, as long as they are not very wide. I do not have specific model recommendations, but you want to start out oozing through the bumps, so look for considerably softer and a little straighter than the Mantra. Mantras can be a pretty good bump ski, if you have the game to stay forward and continually drive them, but not something to learn on in the bumps.
IMO the key to skiing bumps is keeping your tips on the snow, and that'll be a lot easier if your skis are not constantly pushing you back and speeding you up every time you hit a bump. Good luck, and keep those hands in front where you can see'm.