I havnt tried all the variations but use MDF for for the base plate ( hold heating bed )
Then i looked for machine shops in the area and bought a 4mm piece of aluminum the heatbed ( scrap piece for ~ $10 )
They should be able to cut it down to size 300x200mm etc
i slapped on a silicone head bed on the bottom of the heatbed and put kapton tape on the top.
I also bought PEI sheet but Kapton tape works so darn well that i dont see a reason to switch.
Good luck with your build!