He laid her on the lounge and put a mask over her face, which was attached to a nitrogen gas cylinder, and attempted to gas her to death.
When that didn't work, he smothered her with a pillow and returned her lifeless body to bed.
Playford, 55, had also planned to kill his wife but left the house when Sidney's screams woke her up. She walked into Sidney's room to find her lifeless body in bed.
Playford then drove to the Gold Coast hinterland where he tried to commit suicide.
A passer-by found him and called emergency services. He eventually confessed to the murder when questioned by police.
In handing down his sentence today Justice David Boddice said Playford had committed the "most unimaginable criminal conduct", for which there was no defence.
"Your conduct truly involved despicable acts," he said, before sentencing Playford to a mandatory life sentence with a non-parole period of 20 years.
During the court case, harrowing details surrounding the murder of Sidney emerged.
Crown prosecutor Michael Lehane said Playford had lost his job as the chief operating officer of a mining company and was still pretending to be rich and successful.
In reality, Playford was unemployed, crippled with debt and completely broke.
He also cited Playford's pride as the reason he did not go to Centrelink and why he eventually hatched the plan to kill himself and his family.
In an investigation by the Courier Mail, Playford was exposed as a "Richard Gere-type" playboy who had previously spent time in Australian jail for stealing A$100,000 from a former employee. He was jailed for five years from 1988.
A friend of Playford's told the paper he was known as "Rat Face" in high school while another former friend simply remembered him as a "cold bastard".
- with AAP
