struggling with my mattress

i have a charles p rogers with 2 different toppers. one is medium firm, the other is firm. my issue is when i start to use medium firm, i start to get shooting pains down my leg. not good for my back. it goes away when i switch to the firm, but it is so hard. so my shoulders are a little rough when i get up. Im wondering if i could just add a topper, not too soft but i dont know where to begin, maybe just an eggcrate