Maintaining our high standard of living while decreasing consumption may involve reformatting our entire economy as, like you said, ours requires constant growth. However, an increase in sustainable technology is a start. If we consume items that are more advanced and built to last rather than built to break (so we have to buy new ones), perhaps we would not need to consume so much. Still, mother culture has taught us that it is natural to want to consume. This behavior will be much more difficult to change.
Collaborative consumption could also be a step to eliminating mass consumerism because it would allow us to have “new” things without going out and buying something every week. This would still require some consumption, because new items must be introduced to the system if consumers are to be kept entertained. These new items could be made sustainably to further reduce environmental impacts.
I think Rosling’s idea of increasing consumption to increase standard of living and thus decrease population is very feasible, but decreasing consumption overall is essential if we are to live sustainably. Perhaps this decrease in consumption should be added to the demographic transition, implying that those in poverty would have to industrialize and become a mass consumerist society (as long as they are consuming “green” products) before they could decrease consumption. Rosling estimates that if this happens, we could stop population growth around 9 billion people. Technology would have to increase rapidly if the planet is to house 9 billion consumers, so I think consumerism must decrease even if it is green.