Reporting back: apparently a plain 608-open bearing will do the job. Oddly enough, these seem to cost more than the ones with the grease and the covers. Economies of scale I guess.
Not as easy to find: ABEC-1 608 open bearings, as these have a lower tolerance and thus less friction for an application such as this.
Better still would be hybrid ceramic bearings, and then best overall would be fully ceramic bearings, but those come at much higher cost.
If you print mostly functional parts, then probably someday you’ll also want to know. Well, now you know.