Buying a Matress

Hi, You have a great website full of good advice. We are looking for a replacement king size mattress and looking for a pocket spring solution. Our weights are 8-9 / 5'3" and 12-13 stone and 5'11" . We have a wooden slatted bed. I believe we are looking for a firmer option and don`t want it too soft. My lighter wife wants a firm bed but reading our website maybe a medium feel would suit. We have a memory foam mattress currently (I think it`s a Cotswold foam memory mattress its 5 years old now) and find this hot/soft/lumpy and like sleeping in a crevasse now.
I looked at your Origins pocket 1500 , Artisan 1500, Artisan tailored pocket 2000 and Artisan Naturals (should I look at others). I clearly understand the explanation of the quality of the materials used and that they would alter the product price. However, I don`t really understand when I am sleeping on the above said products what difference we will essentially feel. Will I sleep on an Artisan Naturals and say wow this is better than the Origins Pocket 1500 and I`m glad I paid the extra. If I do say this, then why what will be the likely reasons for me saying this? What will I feel from the extra quality materials and cost? Why will my sleeping experience be so enhanced between the above beds when clearly they are all manufactured to a high standard.
Base on the limited info above what would you recommend?
Really appreciate your thoughts and insight in this.
Thanks...Tom