To clarify, on a zip and link bed you have the option of for example, making one side firm and the other side soft. This method of construction can be done on nearly all sized mattresses but there will be a (up to 50%) cost involved. On Ziplinks the cost is reduced (about 20%) as there is minimal extra labour to be taken into account.
To create mattresses with two different tensions a great element of skill has to be employed, What you are asking the manufacturer to do is to place different springs, quantities, qualities, depths, weights etc of waddings and fillings into the same mattress to create a mattress of differing tensions whilst keeping the surface at an equal level. It’s no mean feat and comes as close as you can get to a tailor made, hand built mattress at reasonable cost.
So how do they do it?
There are several different ways of doing this and the main two are detailed below. Before you read those there is an important factor to bear in mind. In order for the manufacturer to know what to put into the mattress you have to accurately describe how different the tensions that you are asking for should be. I mention this because I wonder whether you actually need to go down this route. Read about Soft / Med / Firm Mattresses . However, I find that when people do ask about differing tensions there is a fundamental reason for them doing so. The main reason is usually a large weight difference between couples making it uncomfortable/impossible to sleep together. If so, it may be that you bought the wrong mattress last time and you just need additional help in choosing the perfect mattress for you both without going to additional expense.
The main change a manufacturer can do is to use differing spring counts – 1000 PS side 1 (Firm) and 2000 PS side 2 (Softer) they can also add a firm Saturn pad on top of the 1000 PS to make it firmer still.
The comfort layers can also be adequately be altered without compromise if the layers are similar. For example memory foam can be on one side and firmer Reflex (or any HD foam) on the other. The same goes for Cotton blend pad one side and softer wool blend pad the other. This list of combinations is endless, but only the correct combination can be used if you yourself know how different you want the two tensions to be.
And this will be the main problem with your intended purchase. Will you be able to accurately describe How firm and how soft you want the mattress to be? The following list of questions are the minimum of what I would be asking;
What are the reasons for two different tensions
What tensions do you want?
Do you want to alter the spring count?
Do you want different sleep surfaces?
Finally. In my opinion Milbrook Beds are amongst the best in manufacturing differing tensions on ziplink beds. They do this as a matter of course and so this experience is probably justified in the prices they charge. If budget is not an option then they are at least worth looking at to see what they can do. Alternatively, give me a call and I will do my best to help.