Pocket mattress on slatted base

We bought a firm John Lewis Natural 5000 kingsize to go on a solid bed base and think we should have boguth a medium one. I've read what you say about putting a pocket spring mattress on a slatted base and the neat to put some sort of thin board between the slats and the mattress.
Can you supply king-size slatted base and covering - must be in 2 parts to get up ancient staircase.