My twins have been sleeping together in a pack and play since they came home. We bought it from someone, so it did not come with a mattress or bassinets. To save on space and money, we let them sleep on the firm bottom part with a fitted sheet (for pack and plays). Does anyone else do this? I've had mixed reactions, such as it is too low to bend or they "need" the mattress, to great idea, and the firm bottom is safer. It seems to be working fine, though.