Currently, the American Academy of Pediatrics (AAP) Task Force on SIDS indicates that there is not yet enough evidence to say anything about the potential benefit or dangers of using cardboard boxes, wahakuras, or pepi-pods.
A firm and flat sleep area that is made for infants, like a safety-approved* crib or bassinet, and is covered by a fitted sheet with no other bedding or soft items in the sleep area is recommended by the AAP to reduce the risk of SIDS and other sleep-related causes of infant death. Keeping baby in your room and close to your bed, ideally for baby's first year, but at least for the first 6 months is also recommended by the AAP. Room sharing reduces the risk of SIDS. Having a separate safe sleep surface for baby reduces the likelihood of suffocation, entrapment, and strangulation.
You may want to consider these questions before making a decision:
*A crib, bassinet, portable crib, or play yard that meets the safety standards of the Consumer Product Safety Commission (CPSC) is recommended by the AAP Task Force on SIDS. For information on crib safety, contact the CPSC at 1-800-638-2772 or http://www.cpsc.gov.
Learn more about safe infant sleep environments.