Best Mattress choice for Pars Defect

My daughter has been suffering with back ache for 2 and a half years following a road accident and has been diagnosed with a bi lateral Pars defect, which means she has two breaks in the vertebrae of her spine and it has moved out of alignment causing the back pain and more recently leg pain/numbness. Her current mattress and we have been to Benson's who advised a Sensafoam 6000 which she found really comfortable but I'm not sure after reading about them. Her current base is slatted.