I know that the old RAFM line of figures had both armed and unarmed figures in a naval uniform with the soft hat. The figures are rather "wooden" in appearance and are closer to true 25mm.
Also, Old Glory has naval figures in their Mexican-American War line. They are wearing the flat brimmed hat, which as I recall was being phased out by the 1860's for the soft hat. However, I am sure they would work as well. They are closer to 28mm in size. I know that Old Glory can be a tad "hit or miss" in their sculpting, but these are on the more acceptable end of the spectrum.
If I am not mistaken I also believe that Redoubt had a line of ACW naval figures. I have never seen them, but if they are like the other figures in their lines they would be well done, but on the larger side of 28mm.