Hi geoff
I purchased a good fold up memory foam mattress from Amazon approx at £150, it folds in 3 places the same as the rock and roll bed units but being 6 inches thick the seat cushion protrudes over the front when using in the seat position.( It's the right size when down for the bed )
So I split one section off the mattress along the stitching line and when using as a seat I tuck this (squab) cushion under the bottom of the backrest cushion to allow it to sit farther back.
I have also made covers for this using a single duvet cover
a sturdy canvas bag is also available when not in use
it is exceptionally comfortable.
hope you can understand this and hope it helps
inofia mattress
milliard case