Susan,
Yes, the UV can be an issue with convex glass.
Although we make ours in 3mm and it does block about 35% . . . any light through windows is similarly reduced, so maybe not as bad as one would think.
In saying that, we are attemping to find a UV blocking product to coat our convex glass for framers. Will be an optional service, once we get it out there.
Ok, we make the convex glass and some of the old frame shapes as reproductions (we are in Australia), and so does Inline Ovals (Canada, and I think they have a warehouse US based).
Options are making a rectangle frame in the moulding of your choice, and either using a depth or boxing slightly to take the portrait. Mat up to the shape, and use flat UV clear (or other UV glass) as desired.
Now if it was an oval, you could also do this with an oversize frame, and mat up, same as a rectangle shape.
But from your size, I would say you have the cathedral . . . like this (3rd from left):
Or if the rectangle sahpe overall is ok with the client, we often make up custom size rectangles in convex glass, and the framer uses this, usually in cases where the frame is too deteriorated or damaged, and not one we reproduce.
If it is the cathedral as above, we do repro this frame along with the convex glass. Maybe Inline do too.
Hope this helps. E-mail me if you want to ask anything about your job.