I think your design is very nice and would try to keep all the
elements you have, but as you say it needs to taper in order to be
comfortable for most people. It is definitely easier to cut the
correct profile while it is flat.
Make a brass (or silver, cardboard, paper) template in a wide ring,
taper the ends (now you will see how tricky it is to saw while it is
a ring), file both ends flat (a straight taper from top to bottom
will retain more of the original design), then cut the seam and
flatten it again to have a template.
You may be able to flare the edges while it is flat also; the flares
should remain to some extent after careful bending into a ring.
Hammering to size and roundness will be a problem if it is flared,
but it can be pulled into roundness on a ring stretcher.
Perhaps the flares should fade out to leave the bottom half of the
ring un-flared, then sizing will be straight forward, and it may be
more comfortable between the fingers. Future sizing of the ring is an
essential requirement - either to sell the ring, or later when the
customer needs it.