We have a 2,5 inch medium density foam topper which we are very pleased with, but it's not a Duvaley brand.
Following advice from within the trade we went to one of the UK's major trade suppliers of these foam products for hotels, shop brands etc, Southern Foam.
We visited them to "test" the various densities and thicknesses out, then emailed a drawing of the shape we required and it came a few days later neatly in its "Cool Plus" zipped cover.
We chose the medium of three grades as even that's weight is considerable. Had it for several years and very pleased with it in every respect, going direct it saved on buying a branded product.
Southern Foam have been supplying foam for over 40 years. Foam conversion for furniture, bedding & packaging. Also feather seats and backs.
www.southernfoam.co.uk
They also trade via Amazon:
Southern Foam 3-Inch Memory Foam Mattress Topper Including Luxurious Cover, Double, White: Amazon.co.uk: Kitchen & Home
www.amazon.co.uk