platform for attic that is compact

I dunno, it sounds like a bed board. These are foldable planks made of cardboard, wood, or sheetrock that are ostensibly used to firm up a bed by creating a platform under a sagging mattress. You could conceivably use this in an unfinished, unfloored attic.

-C

You could go to one of the big box hardware/lumber stores and have them rip a piece of half inch plywood to a width that will fit through your attic hatch or door. Trim it to length so you can make the turn through the door if necessary. Have cut two identical pieces and there you go... two tools

You can sometimes purchase Oriented Strand Board (OSB) in sizes of 2 x 8 ft that is tongued and grooved. The usual size is 4 x 8 ft, the 2 x 8 ft size is intentionally sized to fit through an attic door. The tongued and grooved edges allow the pieces to interlock. I floored an attic using this approach.