silenight rio micraciol mattress used on a slatted base

The mattress in question is used on a slatted base the slattes are not sprung and after 3 years the mattress now has troughs in it and its a no turn type what type of mattress should I be buying for a double bed on a limited budget that is why I purchased this mattress online so I am not sure if it will be covered by siletnights 5year guarantee?