replacing lower jockey wheel

Jockey wheels with bushings are pretty common. (NB for readers not familiar: bushings, aka plain bearings, just have the axle rotate within a plastic or bronze sleeve rather than supported by bearings. The bushing materials are self-lubricating.) Also, the plastic in question is a pretty common material for jockey wheels, and it is not intrinsically fragile in that application. That was discussed on a previous Stack Exchange post. Furthermore, the jockey wheel may appear to have relatively high friction when spun by finger, but we don't push the pedals with our fingers. The amount of friction is pretty marginal in the context of your total power output. That said, play in the lower jockey wheel is probably a sign that it's wearing out. Note that play in the upper wheel is by design.

On performance road bikes, one of the minor new trends is to replace the jockey wheels with slightly larger ones, e.g. Kogel Bearings makes 12t upper and 14t lower pulleys for current generation Shimano road groups, which come stock with 11t pulleys. However, the clearance between the upper pulley and the smallest cog is a potential issue, and some Shimano groups can only take 11t replacement upper pulleys. On the lower pulley side, there may be interference between the pulley teeth and the cage.

Thus, extrapolating to your group, if you are dead set on metal jockey wheels, it would be safest to get the 11t pulley. A larger jockey wheel may work, but it's not guaranteed. At minimum, you'd need to provide your derailleur make and model. As described in the first paragraph, I'm not convinced it's necessary for most riders to upgrade to metal pulleys and cartridge bearings. In interest of full disclosure, I did upgrade the jockey wheels on my road and gravel bike to 12/14t Kogel units, which are aluminum with ceramic bearings. That was for performance reasons, but the expected difference in drivetrain friction is small, maybe 0.5-1W at 250W input power. I have typically seen long life out of the stock plastic pulley wheels.