There are many incremental changes you can make to get from 35% to 40% or even 50%. But if you are talking about doubling your savings rate, that means rethinking everything that you probably take for granted -- housing, transportation, food, insurance, travel/vacations, clothing, etc. Because no matter how large your income, if you have gotten used to living on 65% of it, cutting that figure by more than half takes a major readjustment.
Which is why artificial numbers like savings rates are useful only in the most general sense. What really matters is learning that happiness doesn't come from stuff, and figuring out what balance between lifestyle and time in the workforce works for you and your family.