The main obstacle to achieving "sustainability" is population size.  All that needs to happen is for conditions to change enough so that the total population of Homo Saps and our domesticated animals and plants remains at or below .0001% of the total biomass on the planet and the species will be sustainable.  About 2 orders of magnitude, leaving around ~100M meat packages ambulatory at any given time.

A sufficient increase in the Death Rate of people past reproductive age to 99% coupled with a Fertility Rate <1 for females should drop the population down to a sustainable level in a few generations, then after that these two parameters can self adjust to maintain a steady population of homo saps between  0-60 years of age of around 100M sustainable meat packages.

Famine, Pestilence and War will probably accelerate the population reduction so that it achieves a sustainable figure more rapidly, perhaps as fast as within a single generation.  Such a rapid reduction is not ideal since it would be very socially disruptive, but once all the corpses were picked clean by scavengers life would settle down to the new normal.

Quality of life would improve dramatically with the disappearance of fast food, Netflix and Rap music.  The disappearance of smart phones would lead to the gradual rediscovery of sex by teenagers.  We will have only have two genders, people with assholes and people who are assholes.

RE