I will have a pivoting base with 3 fixed casters and a pivot in place of the fourth. I'm having trouble trying to come up with a easy to setup and no maintenance pivot. The weight requirements are not much, at most 100 kg.
I'm considering just using a straight rod down a hole in the base and also on a fixed piece of wood in the floor, with a Nylon/PE washer/spacer between them. This will be much easier to implement and shim to level if needed. I also think that this will be zero maintenance since the friction between the steel base and the nylon will be very small.
This will probably be smoother due to steel ball (not sure), but it is harder to setup and shim to make the base level. I also think that it might have wear faster, but I could be wrong here.