It seems like it would be important to determine why they are bare-backed. If it's the usual cause -- an overenthusiastic, or undercoordinated, rooster -- then salves and dressings are not likely to make much if any difference, a saddle is what you'd want. OTOH if it is from picking, you would want to KNOW to try to get it stopped.
FWIW though, I had a little campine hen very barebacked all last winter (large sussex roo's favorite concubine, what can you do), I kept thinking I'd try to sew a saddle for her but never did because honestly she never acted any differetnly. She did sleep snuggled up under the roo's wing every night (does that when feathered, too), which probably kept her warmer, and my chicken building did not get below the low 20s F last winter so it'd be a different matter if you are getting down to the single digits or whatever; but I just thought I'd toss that out as a data point.
Good luck, have fun,
Pat