According to a meta study on personal greenhouse impact the biggest "less" thing a person can do is to not have too many children. To their data a single child represent yearly the cost in CO2e as is saved by 20 people not driving, 40 less air trips, or about 100 people eating a purely vegetarian diet for the same time period. (http://iopscience.iop.org/article/10.1088/1748-9326/aa7541)

If we want less we need to understand the order of magnitude that the different forms of less have.