Hi Sarah,
 
Thank you for your question.
 
As you require a pocket sprung mattress, and at your body weights, I would recommend that you both have a medium spring tension as this will then give you the correct support for your weights.
 

 
I would need to know the size of the mattress that you require as you have mentioned that this is to go into a loft conversion and the access is quite tight.
 
I would also need to know the type of fillings that you require.  These are all the upholstery layers which are on top of the springs which give you the support.  We have two ranges of pocket sprung mattresses.  Our Origins Range have man made fillings and our Artisan Range have natural fillings. 
 
In the Origins Range I would recommend the Origins Pocket 1500 which is a medium feel mattress that has man made fillings.  This mattress already comes with a medium spring tension which will give you both that all important support
 

 
In the Artisan Range, I would recommend any of the first four mattresses in that range as they all have a medium feel from those upholstery layers.  The difference between them is the amount of natural fillings that is in each mattress.   Our starter model is the Artisan 1500 which has 50/50 natural fillings and man made fillings, the Artisan Tailored Pocket 2000 and the Artisan Naturals both have 85% natural fillings and the Artisan Bespoke 004 has 100%.
 
I hope the above is of assistance but please telephone the office for further help and information on 0161 437 4419.
 
Kind regards Julie