Hi Gareth, 
 
Thanks for your question. 
 
At your body weights we would match you both with a Medium spring tension to get the correct level of support;
 

 
Generally, the advice for aches and pains is to avoid anything too firm in the top layers as this often only serves to exacerbate those pains. 
 
Our firmest mattress overall is our Artisan Bespoke. This has no sort of give in that top layer. 
 
Our Artisan Naturals is our true medium feeling model giving that slight sink into the top layer but not too much. This is also our best selling model as the medium comfort means it's neither too soft nor too firm. 
 
The natural fillings in both these models will give that cool sleep surface. 
 

 
In regards to the current base, we'd advise to board over the slats if the gaps between them are bigger than 3" as this will protect from indentation and damage. 
 
I hope this helps but if you have any further queries please don't hesitate to contact our office on 0161 437 4419.
 
Kind Regards, Lee.