Hi Virginie, 
 
Thanks for your question. 
 
Usually, what we find here is that the best route is a traditional pocket sprung mattress. This is due to the fact you'll be supported by the springs inside and then you have the fillings sitting atop those springs providing the comfort. 
 
At 65 and 80KG we would match you both with a Medium spring tension to get the right level of support. 
 

 
 
Given the scoliosis and the fact you disclose you find your current mattress too soft we'd advise to go for a more medium feel in those comfort layers. 
 
Have a look at our Origins Pocket 1500 and Artisan Naturals. Both are true mediums in the top layers providing a slight sink but not too much. The main difference here is that the Artisan range is constructed using natural fillings; Ideal for anyone who identifies as a hot sleeper. Longevity also comes into play with the Artisan range as natural fillings last longer than synthetic fillings. 
 

 
A true medium in the comfort layers will allow a slight sink and pressure relief. 
 
The base can also make a difference to the mattress - If you found the mattress on the floor to be the most comfortable then we'd advise to go for a solid platform top base that will give the mattress a slightly firmer feel. 
 
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. Our office is open Monday to Friday 8am to 8pm and Saturday and Sunday 10am to 4pm. 
 
Kind Regards, Lee.