Hi Martin, 
 
Thanks for your question. 
 
Every pocket sprung mattress has 2 elements to it; You have the spring tension that is determined solely by body weight and then the fillings that form the comfort layer - These are what sit atop the springs and what your body is in direct contact with.
 
We can't construct 2 different mattresses in the top layers for use together - It's only the spring tension that we can change as we recognise that there may be a big difference in body weights in certain cases. 
 
We can do Zip and Link mattresses; Ideal where there is that big difference in body weights, where you may struggle to flip and rotate a one piece mattress or where access to the property is restricted. 
 

 
Given that one of you prefers a soft and the other firm there will have to be a level of compromise and I'd advise to go in the middle and go for something more medium feeling in the top layers. 
 
I would have a look at either our Origins Pocket 1500 or Artisan Naturals. Both are true mediums in the top layers; The only difference is that the Artisan range is constructed with natural fillings that in turn provide a cool sleep surface. At your body weights you can choose either a dual tension of Soft and Medium or the one tension of Medium. Your wife is borderline between a Soft and Medium spring; If she wants a bit more give then choose the Soft spring but if she wants a bit more support then choose the Medium spring. 
 
Please note that we can do a dual tension in a one piece mattress in the Artisan range. if you opt for the Origins range then you would need to choose Zip and Link. 
 

 
I hope this has answered your questions fully but if you do have any further queries please don't hesitate to contact our office on 0161 437 4419. We are open Monday to Friday 8am to 8pm and Saturday and Sunday 10am to 4pm. 
 
Kind Regards, Lee.