Generate constant voltage sources from the power supply using MOSFET
Unless you somehow manage to integrate an inductor inside your chip so that a buck regulator can be realized, using any form of linear regulator to step down a voltage to a lower level is NOT going to "consume" less power (watts) for the same current drawn.

Linear regulators work by just burning-off the excess voltage as heat so there's no net power saving. Of course, if lowering the voltage also lowers the current then this does give a saving but, at the 100 uA level I think you'll be wasting your time and I would recommend trying to figure ways to make your basic circuits take less current.

That is my advice.