Where to get a decent mattress? (London)

[lowrib]

Where would you go in London to get a (single) mattress?

Would go to John Lewis but they take a week to deliver and we need it for a guest before then.

We were going to get an IKEA mattress, but just read some reviews and they're really bad!

Where else could we go?

TIA

I like Ikea mattresses, but only the top-end ones.

Warren Evans?

Thanks both of you.
We're going to have a look at Warren Evans. Been totally put off IKEA I'm afraid!

Feather and black, expensive but worthit.