What would be wrong with a urethane bushing? I believe it would also help absorb some shock. Even the UHMW is hard for a bushing material.
They definitely need grease grooves. I have to have custom sleeves and bushing made from bronze for equipment at work.
I have found that a radial groove at about 25% from each end, with longitudinal grooves to connect them work really well.
It allows grease to stay in the full circumference of the bushing.