The most sustainable economy would be one in which the goods consumed in a region are produced in the same region using local resources and local labor. Ernest Fritz Schumacher referred to such a system as “an economy of permanence.”
More about E.F. Schumacher who coined this term:
Kumarappa was a close associate of Gandhiji and a firm believer in the theory the village must be made the focus of economic planning. Aware of the dangers of unchecked industrialisation. You can read his book here:
https://www.mkgandhi.org/ebks/economy-of-permanence.pdf