Defending Australian Open champion Naomi Osaka said on Saturday that 2019 was the "toughest year of my life" after the Japanese ploughed through several coaches and suffered a major dip in form.

The 22-year-old began last year in spectacular fashion, winning in Melbourne for back-to-back Grand Slam titles and soaring to the top of the world rankings.

But she then exited Roland Garros in the third round and Wimbledon in the first round, and her defence of her US Open crown similarly fell flat.

The Japanese roared back with titles in her native city of Osaka and then in Beijing in the autumn, and in December hired the Belgian Wim Fissette as her coach — her fourth in less than a year.

The world number three, who faces Marie Bouzkova of the Czech Republic in her opener in Melbourne, said she was "in a better head space" compared to 12 months ago, and playing better tennis.

"But honestly, last year was the toughest year of my life, so I would hope it gets better," Osaka added.

Pushed as to what she meant, she said: "I guess just before everything (success), if I lost, it wouldn't be a (news) article.

"Now if I lose, like, there's news. It was tough adjusting to that."

Osaka described herself as "a bit more seasoned" compared to a year ago and hopes feeling more relaxed can bring success, starting with the defence of her Australian Open crown.

"Last year I feel like I was young," the Japanese said was a smile.

"I was just this young kid that was going out. My goal was to win and I wasn't going to let anything stop me.

"I feel like now I appreciate more every single win because I know what it took to get it.

"Of course I want to win every match and I want to go out there and do that.

"That's what I'm here for. I think maybe last year I was a little bit more fearless."

Osaka, who has been open about her struggles with the pressure that comes with success, says she is trying to ignore what is said and written about her.

"I've been training my whole life for this (tennis)," she told reporters.

"I shouldn't let outside noise — no offence to you guys, love you guys — but outside noise dictate how I'm feeling."