Hi Adam, 
 
Thanks for your question. 
 
What I always advise is that different retailers will have differences and then similarities. Our Artisan comparison models we use for Vi-Spring will give a good idea of what our own models will feel like and this is the same for spring tensions. 
 
Every pocket sprung mattress has 2 elements to it; The spring tension that is determined by body weight alone and then the fillings that sit atop the springs. In both you can have a soft, medium or firm.
 
Please see below for our guidelines on spring tensions and body weight;
 

 
It is difficult to get a good idea of what a mattress will feel like in a showroom because they will have been sitting there for a long time and tested by many different people of many different body weights. This will always soften down the feel of the mattress quite quickly. Pair this with the fact that most showroom mattresses are generally paired with a sprung base and this gives it an even softer feel. This often accounts for the differences that some people feel when testing showroom models in different tensions. 
 
If you are trying a mattress in a showroom and you have a solid platform top base then we always advise to ask the showroom to place the mattress on to the floor. This will emulate the solid platform top feel. If you try the pocket sprung base in the showroom but you have a platform top base at home then you are going to have a completely different feel not to mention an inaccurate one. 
 

 
I hope this has answered your questions fully but if you do have any further queries then 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.