Advice on wood please

[crappyday]

I'm trying to make a cabin type bed for my daughter. She has a built in window seat that I'm hoping to convert into a sleeping platform.

I therefore need a piece of board which will rest on the window seat (3 sides of the bed) to support the mattress. It needs to be strong enough for her to sleep on, and rigid enough to not sag on the 4th side which doesn't have the seat underneath.
I will be putting an ikea unit under the fourth side, but it will not be high enough to support the board (by about 5cm).

I have no idea what type of board to use, and what thickness. Help!

Options from b&q seem to be scaffolding boards, MDF, ply.

I'd rather have one big piece, rather than several pieces so they don't move about.

Any pearls of wisdom anyone?

4"x2" planed timber will suffice. I'd probably use slats (recycled from an old bed if you (or anyone else has them) or 12mm MDF or Ply - cut to size if you can transport it home. You'll likely want some tile batten to fix to the inside of the 4"x2" to give the board/slats something to sit on.

I think you can buy just the slats in ikea,they come with a fitting set that allow them to have a bit of a bend in them and therefore a bit of spring, making the bed more comfortable, the only issue with that is ikea beds are not standard size so you would need to use one of their mattresses. Other than that, you can use MDF or Ply as suggested above. Ply would be lighter but need more support. B&Q will cut to size for you.

Lucky DD :) I would love a bespoke cabin bed for her but my DP is a carpenter so lets face it, it aint never gonna happen too busy making other people's houses look wonderful

Timber is restricted in width due to the width trees grow, so one big bit of wood the size of a mattress does not exist unless its processed e.g. MDF, Ply etc. MDF and Ply both do bend, but they are very strong. If you've ever seen a long bit stood up and lent at an angle you'll see it bends in no time.

Beech is strong, sofa frames are made from it. Could you use multiple slats like a wood bed? (not sure I understood how it will be built, so apologies if that wont work)

And you can order timber cut to size from lots of places online too e.g. www.timbercut4u.co.uk

Thanks all. I've settled on ply I think. I think it'll need extra support on the unsupported side as its a long side but will use some blocks for the time being.

can you raise the Ikea unit on some blocks or legs so it gives a bit of support?