Hi Malcolm, 
 
Thanks for your question. 
 
You don't necessarily need to purchase a new base when purchasing a new mattress. Our advice is only to purchase a new mattress if the existing base is faulty or you want to specifically replace it. 
 
With ourselves the guarantee is in no way affected. However, other retailers will be different in the sense that they will try and force the sale of the base at the same time. 
 
A solid top base will give any mattress going on top of it a slightly firmer feel.
 
If you would like any advice on our pocket sprung mattress ranges (Origins and Artisan) please don't hesitate to contact our office on 0161 437 4419.
 

 
We would need to know your body weights, sleeping habits and preferred feel in the top layers to discuss suitable models.
 

 
Kind Regards, Lee.