Our mattress feels firmer than the one in the shop?

Could you please give me a price for a sprung edge divan base that would be suitable for a Harrison mattress . The mattress I have is a Trebah with 8200 springs in it. At the present time we have it on a Nolte sprung slatted base and are finding it quite uncomfortable, although in the shop on the divan base it did not feel as firm. Please could you advise me if the base could be the cause of the problem. Please could you give me a price for 2 Drawers and also without, for a King size. Thank you very much. Gill Atkinson