My first DB trailer was an adapted runaboat trailer.
I stacked conventional rubber rollers for the tail roller and it worked.

My current DB trailer is a Baker and they use a 2-1/2" dia. galvanized steel tube with bearings on each end.
Industry-standard stuff.

When you're trying to load in a heavy cross current, a big, wide roller on bearings is a nice thing to have.

When the boat on on the bunks it is off of the roller.

I would look around for a roller like that if the budget allows.