Dear John Ryan Contemporary,
I found your article after a desperate search online to find the answer to my problem.
I have an inexpensive, but excellently-kept solid pine slatted 4'6" base (the slats are 12cm apart and there is a thick central wooden support column/block at right-angles to the floor) which for 20 years was partnered with a simple foam mattress and I had no issues whatsoever with the bed as a whole. I am a single lady, petite, weighing 7 stone and the old mattress never rucked, dipped or sank.
However, I felt that it was probably time to replace the mattress as, for the last three years I have developed an unexplained chronic low back pain (actually in my coccyx), and although the mattress was not known to be contributing to my pain, I thought that, due to its age, it was probably a good time to replace it.
After months and months of searching I finally decided on a Tempur pocket sprung mattress costing £560. After just one nights' sleep however, the mattress dipped in the pelvic area by 5cm. An impartial mattress team came later to inspect it and the diagnosis was that the mattress was faulty. They had a good look at the base so it cannot have be unsuitable or they wouldn't have decided that the fault was in the manufacture of the mattress.
The mattress was returned and I was refunded. But now I had to find another mattress. Rather than go for another Tempur (once bitten...) I went instead for a cheaper (but still equally comfortable and good make) Silentnight Pocket Essentials (1000) mattress costing £200.
I have just spent one night in it and - horror or horrors - I awoke to find that middle has a slight dip to it!! Surely I can't be unlucky twice? Is this the 'hump back bridge' effect you mention?? Yet my base has solid slats, not sprung ones - also I am very light! - and the mattress is not protruding through the slats on the underside. I am puzzled, perplexed and distressed at having this experience twice.
Why is this happening? Have I unwittingly ruined the mattress because of the base? Could the problem sort itself out if I go out and get some MDF to cover the slats today? Will the dip go?.. Please help... Thank you.