Hi Tony,
 
Dependent upon how long you have had the current product, there may still be an opportunity to exchange with the retailer for a firmer version. If this is no longer possible, rather than buying a new mattress, you could try placing some board, around 10mm MDF over the base, which will make the mattress feel firmer. I am not able to advise upon which mattress you ought to look at without knowledge of your body weight and preferred feel and if you would like to call our office with these details, we will be able to provide further advice.
 
Kind regards.