His mum and dad, who are both 24, were initially arrested on suspicion of murder but have now been released without charge as the police deemed the little boy's death a tragic accident.
They are still not sure exactly how Harrison became trapped by the mattress, but said the parents are "completely exonerated" from any involvement in their son's death.
An inquest will now be held to try and establish the facts. Officers were first called by the ambulance service at around 9.30am on Sunday after paramedics were called to the family home. A post-mortem revealed that Harrison was asphyxiated.
Locals described the family as 'nice' and 'happy' and said they have another son, Caleb, aged four. Neighbours said they doted on their children, and looked after them well.
A spokesman for Lancashire Police said: "Detectives wish to pass on their sympathies and condolences to Harrison's parents, as well as his wider family."
Such a tragic story.