Wow, I'm afraid that the price of that mattress in John Lewis store just reflects what the top people in the UK are willing to pay out for things. Which in truth also reflects the wide disparity of peoples incomes and that there is a growth of those earning higher incomes, possibly as a result of the shareholdings in what used to be public owned businesses such as Royal Mail, Water, Gas, Electric, Rail, Bus and others etc. These have been paying some huge dividends over the years as a result of the huge increases in their profits and also of course of the so-called windfall profits.
Then have a look at the other end of the scale, the gig-economy, where you earn a pittance and if you're lucky may even get to work a 40-hour week.
One of my sons works in the retail sector where most are on either zero or low hour contracts, he is on a 6-hour contract but often does about 15 to 20 hours a week. My other 2 sons, both work 40 hours a week at the same company, in different sections of the business and have differing terms of employment and conditions earning gross between 20k and 30k gross, hardly a fortune.
John Lewis is a store that does tend to cater more for the higher income families, a more realistic price for king-size mattresses can be found here
https://www.mattressman.co.uk/mattresse ... _Price_Asc where there are no fewer than 240 mattresses to select from ranging in price from £140.25 to £2,719.15, poles apart from the John Lewis price.