Opinions on a reduced Dreams Insignia Blenheim 4000 Mattress

Hello there,
I read an answer you gave a while back when someone was comparing the Dreams Blenheim 4000 £1300 to a John Lewis 4000 at £800. You reckoned the Blenheim was very overpriced and lesser quality. The Blenheim is now discontinued, but a shop near me has an ex display one heavily reduced. I found it very comfy and is hardly marked from display, however it does not come with a warranty now. Do you reckon the quality is there to last me the 8 years its designed for? Its down to just under £800, but I know there is room for negotiation. what should I aim for or should I be waiting for John Lewis or M&S sales instead?
Thanks