Hi Graham.

Ha, Holy Grail - We like being refered to that way! As you have probably read on other comments, it is impossible to find a mattress using one tension spring that will suit two people of differing bodyweights.

The reason you liked the Vi spring Classic Bedstead is that it offered you the chance of dual spring tensions. We have an article on these dual springs here.

However the salesman's explanation of half Soft and half Medium is relatively correct in some way. There was an explicit piece of information missing from his explanation that puts your Medium and Firm thinking into perspective. The Classic Bedstead is not listed on the Vi-Spring site and so a precise breakdown of the model you tried is not possible.

For the purposes of this exercise, I shall use the Bedstead Realm as the example.
Vi spring Bedstead Realm: Oct 2012 Official Description

Springs: 1.52mm wire springs, 54mm in diameter, sewn in individual calico pockets and hand-formed into a honeycomb-nested unit.
Upholstery: Upholstered with a wool spring protector pad, then 1,350gsm bonded British fleece wool and cotton, overlaid with 300gsm British fleece wool, 200gsm bamboo and finally 900gsm of blended British fleece wool and cotton.
Cover: Your choice of finest quality Belgian ticking from the Vi-Spring collection.
Tufts: Hand tufted with felt washers.
Spring Tension: Each of Vi Spring mattresses come with a standard spring tension allocated to a particular model. In this case the Vispring Bedstead Realm the spring gauge is 1.52mm with a spring diameter of 54mm.

The question is, is this 1.52mmm spring gauge attributed to the Soft, Medium or Firm mattress on the display floor? Unless you (or the salesman) know this detail, it becomes rather difficult to assess which mattress tension (SMoF) would be suitable for you. To complicate things further, the spring gauge has to be taken into consideration with the upholstery used.

In the case of the Bedstead Realm above which has a predominance of soft upholstery (wools and cottons) the spring gauge is rightly on the higher side (1.52mm can be considered as a medium spring tension - conversely, 1.28mm can be considered a soft gauge) As a means of explaining this further, The Vi Spring Bedstead Supreme has an element of horsehair within the upholstery.

As this can be deemed to be a relatively supportive upholstery component, the spring gauge is reduced to 1.42mm - but again, this gauge is not attributable to any overall tension SMoF. It has to be said that we too do not attribute our spring gauges to any particular mattress tension rather than attributing them to a weight range as seen here.

I am sure this is what happens when you visit a Vi Spring showroom and as the lowest spring gauge Vi-spring do is in the region of 1.28mm (considered Soft) it is likely that the salesman you spoke to was absolutely correct in his recommendation for your wife.

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As for you, and also depending on the actual make of the mattress you tried it could be either medium (approx 1.40mm) or Firm (1.50 - 1.60mm). As you can see, differences in spring gauges are in the tenths of millimetres - diameter also comes into play and also the upholstery component build has an overall effect.

Don't get too hung up on this for the moment - they are important factors, but they should be addressed when you have decided upon a particular model. The first thing you should do is to set a realistic budget and see what that can actually get you. I would advise you give us a call to address which split tension mattress would be suitable for you.

All the best

John and Ryan.