Mattress topper on slatted bed euro king size

Hi - I purchased a Habitat slatted bed frame in Euro King Size (Fleur - no long for retail) and when I moved bought a Relyon Mattress, 2000 spring coil. I've previously had a top grade divan bed/mattress with a Relyon mattress it was wonderful but it was ready for replacement after 18 years of use. This current mattress is not as expensive as the previous was one was (relatively) and after 3 months am still waking in the night with my back aching unbearably as the bed is so hard. I've tried walking and jumping on the bed with my girls in an effort to soften it up to no avail. Would a topper help in making the bed soft? I really dread going to bed and wish I hadn't disposed of my previous bed.Hope you can provide some help!Rosie