Ikea Toddler Bed Compatible Mattresses?

I would like to use a passed down IKEA extendable toddler bed, similar to the MINNEN bed, however I need to buy a new mattresses. The smallest size setting for the IKEA toddler beds is 47.25 inches long and 38.25 in wide. The mattress comes in three sections to accommodate the 3 size adjustments. American standard toddler bed mattresses are about 52 inches long and 26 inches wide. The IKEA mattress is made from polyurethane foam (Ticking: 62 % cotton, 38 % polyester
Comfort material: Polyester wadding, Polyester/viscose (rayon) fiber wadding, Polyurethane foam 1.5 lb/cu.ft.). The description says it is hypoallergenic and the whole mattress is washable. However there is no mention of the mattress being Greenguard certified or what chemicals they use as flame retardants, as many American mattress descriptions say. I also could not find any customer reviews or link to ask product questions. I am nervous to purchase this mattress because I have heard that polyurethane is not healthy and I don't know what chemicals have been used on this product. I am also afraid that when fully extended, the mattress won't be comfortable because of the partitions from the three pieces. I tried looking for other mattresses to buy but I have not found one that is the correct size. Thus I have three questions for anyone out there: 1. Does anyone know if the materials and chemicals used on this mattress are safe? 2. Is the mattress comfortable when two or three of the pieces are used? 3. Has anyone found a non-IKEA mattress that fits this bed? Thanks!