You could try clear nail polish, after all nails are flexible. I
have a damascus steel bracelet that I coated with clear nail polish
on the inside and it works fine but that is a very toothy etched
Metal prep is really important before applying finishes, absolutely
grease free and some roughening of the surface so the finish can
Craft stores yield a lot of different kinds of clear coatings and
finishes that might work. Acrylic finishes are flexible, they're
plastic after all, but some if not all acrylics are formulated with
ammonia which could have an adverse affect on metal.
Have you tried wearing the brass bracelets with no coating? I have a
bracelet I made out of brazing rod back in high school- I won't say
how long ago that was but suffice it to say that there has been a
very long test period and it doesn't turn green or turn me
green...no special treatment or care. I would think that different
alloys of brass may be less of a problem than others and it is known
that peoples own chemistry affects metals in different ways.
Generally, a bracelet doesn't have as close contact with the body
that a ring would
Or you could gold plate.