Do you know the value if this need?

In the UK you see the "Royal Warrant" on all sorts of things, from jars of mustard and packets of cookies to mattresses. It means they've got one at Buckingham Palace too. It doesn't add extra value to anything - all you've got is a mattress. It is generally a sign of good quality, however, so you've got what used, at any rate, to be a good mattress, along with thousands of other people with similar mattresses (or jars of mustard).

You have an old matress! There has not been a king since the early 50s