I have some filament spools that are made from cardboard with a metal tube in the middle. I found these spools would snag on the Ultimaker filament holder so I made these brackets to hold a couple of 608 bearings. Now the spools turn very smoothly with no snagging!
Print out two of these and slot a 608 bearing onto each. Then slot them into the top of the existing filament holder with the bearings facing outwards and away from each other.
They can be removed easily when using smaller spools.