which mattress to consider

I am looking for a new mattress, I have a king sized slatted wooden bed with a very old mattress, i am suffer from back problems and we need a new mattress, my weight averages between 9.5 to 10 stone but my husband is 14 to 14.5 stone, I feel we need a split mattress - please can you advise and is there anywhere we can try then e.g. a showroom / retailer
Thank you