Rakaua Rawhira Rongen was found dead in his parents' bed on the morning of October 15.
In his formal written findings, coroner David Crerar said baby Rakaua was born four and a half weeks premature on August 7, 2011. He weighed about 2.59kg at birth and remained in hospital for six days before he was allowed to be taken home. Despite being premature, Rakaua had thrived and was a "healthy, happy baby".
Father Jorg Rongen looked after Rakaua on the evening of October 14, 2011 to give mother Tania Nahona-Lyall a break.
After feeding, Rakaua went to sleep shortly after 11.30pm, waking about 3am. After Mr Rongen changed his nappy Rakaua did not drink or settle so he put the baby to sleep in between himself and Ms Nahona-Lyall where they slept in their shared bed.
Mr Crerar said Mr Rongen described Rakaua's sleeping position as "his head and back were lying on my upper arm/shoulder area".
He was then quite settled.
After being woken up by Ms Nahona-Lyall about 7.45am, Mr Rongen discovered Rakaua was not breathing.
Ambulance staff could not revive Rakaua and he was taken to Southland Hospital were CPR was continued.
A pathologist's examination classified Rakaua's death as a sudden infant cot death.
During the inquest hearing one of Rakaua's grandmothers emphasised the parenting skills of both parents. She also raised the possibility Rakaua's breathing was physically impaired.
Mr Crerar said that although an autopsy did not reveal any impairment, he could not rule it out.
Specialist paediatrician Dr Villiame Sotutu said Rakaua's sleeping position - asleep on his father's chest - may not have been ideal.
Mr Crerar said coroners had considered several "co-sleeping" deaths in the past few years. In Rakaua's case, he could not find the exact cause of death. He found baby Rakaua died of cardio respiratory arrest classified as a sudden infant cot death.
The death occurred suddenly and unexpectedly in an unsafe sleeping environment with other physical contributors. Mr Crerar said there was no evidence a specific risk caused or contributed to Rakaura's death. He recommended the Ministry of Health should "strengthen and broaden" advice around infant care practices and safe sleeping environments. He hoped publicity to the risks would help reduce similar deaths.