Well rigidity is always a help. Using glass has solved the stickage issues for me on TOM and prusa. The actual surface of glass is probably an option. But Aluminum and glass are best. But, as I learned there is no heated bed formally designed for this. The one on thingiverse is nice but not a kit even though it looks well designed I would prefer that it be an actual kit of qualified parts so I have a lesser probability of errors. Also, maybe a PCB that is designed for the area of the Ulti build surface. Since PLA will not withstand the heat of many of my parts (LED mounts in many cases) then I need to use ABS so this is rather important for me.