Get my nails, a hammer, and a cross....

, jk
If you like the Roto flats go for them, I'm sure you wont need to worry about the roughness, especially so as the board is epoxied.
Rotos Trubass is also an excellent string for fretless, kind of a fake double bass sound (if that would fit).
Otherwise you could take your pick from any other flats without worrying about wear, or some of the smoother Nickels (sunbeams, Dunlop etc).