Way out of the box presure system...

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.