did you consider narrowing the frame down for a 36" wide door, use a
door with a window for light, even if a small window in the top of the
door, fill in gap on each side of door with solid materials (maybe
even pillars, split vertically and put 1/2 inside and/or 1/2 outside)
or 4" glass block on each side?

I do not want to use any type of "filler" materials around the door. Our
home has a "rustic" decor with knotty pine walls on the inside, and a rough
sawn lumber on the exterior.

Whatever door option I go with will have glass panes in the door to let in
the light as the window currently does.

Thanks,

Anthony