Another out there concept... this won't work with the muiulti segment tank of the last wild idea, but will work for a single tank.
In a H2O2 rocket 80% of the propellant volume is H2O2, so you need to pay more attention to the H2O2 side than the fuel side.
Leave a small space at the top of the H2O2 tank. In this space put a solid silver screen/catalyst hung from a thermally compatible string. Unwind the string into the tank letting the silver decompose the H2O2 pressurizing the tank, raise and lower the catalyst to control pressure.
Fuel is pressurized with a bladder from the gas in the main oxidizer tank.
Main propellant valve is a simple burst disk.