Personally I hate all swivel wheels. You push one direction and it goes in a different direction. Two fixed and two swivel wheels is my preference with the swivel wheels being locking from rolling and swiveling. Also I tend to use 4" wheels on heavier items so they roll really well, plus I like to lift them enough so my vacuum nozzle fits underneath.
With that said I welded some plates to the bottom of my small old Powermatic 6" jointer and used 3" wheels I already had. I built a frame for my tablesaw with 4" wheels. Do you have a welder? That would open up lots of options.
Otherwise I would look for a rolling base that has all metal construction that doesn't use plywood. The one by Powermatic that fits perfectly and costs a fortune is guaranteed to work excellently.