Hi Becky,

Thank you for your question.

I can't find the exact mattress but the 5000 model on the John Lewis website is a medium pocket sprung one sided mattress, this is assumed as its states its rotate only. Putting the one sided mattress issue to one side my advice is around the slatted base. Given the issues you have had I can only put these down to your slatted base.

Yes, a bed specialist should of asked this before purchase but unfortunately it is an area of mattress advice that many people miss!

Sprung slats are where the slats are humped or arched.

There are many anecdotes on this site and throughout the internet where the mattress develops a central dip known as ‘The Hump Back Bridge Effect’ and this can easily be attributed to the use of a slatted bed frame where the pressure of the slats (the arches) are too firm to ‘give’ under the weight of mattress and user and, therefore, the mattress is prone to settling on the central support bar.There are of course associated reasons why this happens. The mattress itself can be so unsubstantial and lightweight that the arches on the slats are pushing the internal spring unit out of shape. The underside wadding of the mattress (one sided no turn) has such an inadequate level of support upholstery that the springs are practically forming on to the slats.

Our advice is always to board over the slats, if possible. If the base has sprung slats we would advise that the horizontal slats are boarded over.  We advise either MDF or plywood to do this.  Pegboard can also be used to aid ventilation, though bear in mind the weight of the mattress and what it is resting on.

This should resolve your problems Becky, if not I would get back in touch with the store and raise your complaint as it shouldn't be dipping based on your weight and the relative newness of the mattress.

If you require any further information please call the office on 0161 437 4419 to speak to our friendly team.

Kind regards,
Amy.