Yeah, Boori cots are bigger than most and need a bigger mattress but like others said, you can easily get them from a baby shop. I think ours is Love n Care mattress and was about $100 when we bought our nursery furniture.

It helps to buy sheets that state that they fit Boori cots too. I've bought cot sheets from Target and it's a real squeeze to get them on. The larger sheets are a lot easier! There are a few brands that specifically state they're big enough for Boori cots, usually found at the baby shops. Same goes for mattress protectors.