Artisan Natural or Tailored Pocket ?

having been disappointed with our last 4 mattresses - Memory Foam, AeroGel, Sprung with Topper we are looking to invest in something that will last us more than 18 months.
I am 6'2" and 15 & 1/2 Stone, my wife 5'6" and 11 &1/2 stone. I prefer a firm mattress as have a back problem in the lumbar region, my wife likes something that is cooler and medium firm as she sleeps on her stomach - although with some mattresses this causes her aches in the arch of the back.
We have been looking at the Artisan range and are confused as to the benefits the Natural would offer over the Tailored Pocket, or indeed would we be better considering another mattress?
Can you help or advise please ?
Also - what are your lead times ?