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.
Environmental 
This topic reminded me of something I learned about a few years ago, a Cornucopian viewpoint. (http://en.wikipedia.org/wiki/Cornucopian) Basically this is the viewpoint that mankinds continued appetite for materials and consumption can be met and matched by our advances in technology. This view is one I think that appeals to a lot of people, because if technology keeps on providing what we need, then drastic changes in our lifestyles wont be needed. Now do I agree with this view? Not entirely sure, though it is a very attractive one.
Consumption of goods is something that is going to happen as long as there are people on Earth. I believe that it is going to be tough to change peoples mind when it comes to consuming products that are more environmentally friendly or sustainable, especially if they are already accustomed to a specific product. For example, Nike shoes are not the most sustainable shoes out there but they are by far the most popular. There are programs out there such as recycling programs where the soles are reused, and I believe if that program is used in collaboration with Nike shoes there would be a more sustainable view of Nike and the shoes that everyone wears.
While I agree that both population and consumption need to decrease, I feel that we need to take more extreme view. 9 billion people is several billion people too many. While it is a reasonable and noble goal to stop population growth at 9 billion, if we hope to maintain our species without completely sucking the marrow out of the earth, our population needs to stabilize at a much lower number. Agriculture, in particular, might provide the greatest limit to our population, since our currently growing numbers are largely supported on a culture of monocropping and genetic modification. If we hope to eventually transition into a “greener” more sustainable way of life, which allows the earth to recycle and replenish its resources, we must reduce both population and consumption drastically.