I received a wheel on a used bike that had this conversion done to the rear parallax hub, and it was a disaster, unusable.

Nuke-Proof used to adapt a Shimano freehub body to use a cartridge bearing. I'm not sure what in the way of machining was involved, but they used a threadless axle.
You didn't mention what hub you have, but many hubs would not have room inside the shell for the added OD of a sleeve.
And you wouldn't want a cartridge bearing's inner race resting on top of the axle threads, that's for sure.

Also, if one side is converted to a radial-groove ball bearing, it couldn't be paired with the original angular contact bearing on the other end of the axle without immediate bearing damage under load.

This project would involve a lot more work than would replacing the hub, with no discernable advantage.