My design walls (yes, plural!) are all covered with fleece.
Before I made my first, I tried all the different covering options, painter-taped temporarily to a wall, to find that the fleece seemed to have better hold-power than the flannel, batting etc. My really big one is permanently mounted on the wall, using tentest as the base, then the fleece. I have another smaller, but still large, mounted on a wall which is corroplast covered with fleece. Then I have others not mounted, that I can lean against the wall, again corroplast for the base.
Good Luck with fine tuning your new wall ... and ENJOY using it!