Mattress Inspection Advice on faulty mattresses & beds

I would like some advice on a Hypnos Bedstead Six mattress. I bought it new two months ago along with a new Hypnos platform divan base. After two months, the mattress has sagged badly. I'm not getting a full nights sleep on it and I'm waking around 4-5am with pain in my shoulders and hips. Lack of sleep is really affecting my health now.

I laid my mop over the mattress and measured the sagging to range between 3cm-5.5cm deep, under my shoulders and hips.

Hypnos sent a technician out and I was somewhat surprised at the process as I was expecting a thorough examination of the issues I am facing.

He arrived here and took a look at the mattress. Without prompting from me, he said he could tell by the visible sagging that I was sleeping on the mattress alone and that it had been rotated regularly. I confirmed he was correct.

He laid a piece of string across the mattress in two areas, which avoided the sagging areas, then took measurements using a tatty piece of card propped up. However these were from areas of the mattress with no sagging, so naturally they show there is no problem with the mattress.

He lay on his back down the centre of the mattress and said it felt fine and there was no sagging. I asked him to move over to the area with the visible sagging. His body noticeably sunk and he said that did seem to be a problem, then backtracked and said that was normal wear and tear for a year old mattress. I said it was two months old. He said it was delivered to me on the 14th November 2020 and I must have had nearly a years use out of it. I confirmed it was ordered in August and delivered to me on the 17th August, so it was only two months old but I did notice that the mattress has a manufacturing date of 20th September 2020 on it.

I asked if he could remeasure the area where the sagging is worst but he refused to do that and claimed there’s nothing wrong with the mattress based on his initial calculations. He said it was my fault for sleeping in a double bed and I’d be better off with a single, then said he was in a rush to get through his calls and left.

The whole process took about five minutes and was clearly engineered to write a report in Hypnos favour.

I bought a new mattress expecting a comfortable and restful nights sleep. I cannot sleep on this mattress due to the sagging. It’s not supporting my body and I’m waking every night in the early hours with pain in my shoulders and back. It’s not fit for purpose.

The retailer has stood by the "independent" report and said there is nothing wrong with the mattress and nothing they can do. I've had no further response from Hypnos.

Can you offer any advice on what to do next? I've spent almost £1000 on this mattress expecting a comfortable nights sleep, but I'm not getting one.