Depends bhai where you playing, over in the UK bowl hardly comes chest high. In Aus it probably comes a lot higher. Back home i dont even think you need a helmet LOL
But learn to play the short bowl, duck or sway what ever your better at, even if your a lower order bat. You might have to wear one or two bruises its not an easy game but a chest guard not necessary gets in the way when your out in the middle for a while, running etc and general flexibility. So maybe buy a cheap 1 really cheap 1 for nets, practice with friends ducking pulling etc. And when your in the middle you should be in good groove not to need one.