UOMEUR Full Box Spring 5 Inch Box Spring for Full Bed, 3000lbs Heavy Duty Metal Mattress Foundation Support with Easy Clean Fabric Cover,Non-Slip/Easy Assembly/No Noise

I believe most ikea beds are platform beds. A box spring is about the same size as a mattress and covered in the same fabric. It's made from wood, and fits into an angle iron frame with legs. Pictures here.