Hi Graham,
 
Thanks for your question. 
 
At your body weights you will need a split tension mattress to get the right level of support each. 
 
You will need a Firm spring and your partner will need a Medium spring;
 

 
You both being a side sleepers need to avoid anything too firm in the top layers as it will only cause pressure point pains in places such as shoulders, hips and knees. 
 
I'd advise you have a look at our Artisan Naturals or Bespoke 004; Both are true medium feeling models in the top layers providing a slight sink in sensation but not too much. The main dfference between them is that the Bespoke 004 has a full 100% natural fillings giving the coolest sleep surface you can find. 
 
Please note that a Euro Double size is 140cm x 200cm whereas a standard UK Double size is 137cm x 190cm. 
 
As such we can do this size for an additional 20% on the cost of a standard Double as we need to increase both the width and length. As these are non-standard UK sizes there is subsequently no 60 day love it or return it guarantee on it as we have limited resale ability. 
 
Those mattresses are fine to go on to a slatted base as long as the gaps are no bigger than 3". If they are then you will simply need to board them with some plywood, pegboard or MDF. 
 

 
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.
 
Kind Regards, Lee.