Silverleaf Residence style one will look best. May I suggest this one from Anthropologie in Silver https://www.anthropologie.com/shop/gleaming-primrose-mirror2?category=mirrors&color=020

Thank you Tessa Rose Design.

Would you suggest I get the
5': 60"H, 50.25"W or
7' : 84"H, 64.25"W
for the 75” wide mantel?

The largest one.

Thank you for all your help Tessa Rose Design!

Usually mirrors are there to reflect something or make something look larger. Look at what is reflected in your examples.

I would add art. It doesn't have to be super big, because you don't have to fill up the space.

Beverly, I completely agree with what you said. It's pretty, but not for my room. Thank you for mocking up my fireplace with the 3 different shaped mirrors. I like the round and found this one framed in gold leaf. It's 42". Maybe it's not big or substantial enough? Any other ideas?

Thank you for your input, Kathi. We have open space with plenty of nature behind our house and lots of windows so the mirror view will be nice.

What will the mirror reflect/double? Something interesting or beautiful? Maybe just the ceiling or another wall? Art is the #1 go-to thing to hang above a mantel.

Art. Mirrors are out of date. Unless it is to make the room bigger or to use in the morning to brush your hair, artwork is the best option.

Go with your lamps, 75” wide. From shades of light

Sorry this is off topic, but your wood floors are so pretty! What type of wood is it, and what type of stain did you use? What type of finish did you put on it?

I like the first one for the space.

At 42" you'll have 16.5" of space on each side. You might want to consider some type of gold leaf candle holder for balance.

I couldn't find gold leaf candle holders so I just included these below so you could see the difference.
I think you have to be careful about your selection because the scale of the fireplace surround is so very bold, the gold leaf frame looks a bit lost.

BTW I don't think I would place more art next to your other painting unless the medium was quite different.

These textured squares from Crate & Barrel

If you Try something like this you will be able to change it up every once in a while

Put vertical art over the mantel. What would a mirror reflect? You don’t need to see your room reflected in a big mirror, and a mirror across from big windows will reflect all that light into the room. Add draperies with some color and a large area rug.

Loobab, my floors are Santos Mahogany. They have worked out well for us.

I had to laugh, Adam. Mirrors are out of date? Really? I guess I’m out of date and I like doing things my own way, maybe it’s the UC Berkeley in me. ;)

I found this mirror that is 48" square. Our firebox is 42" wide and mantle is 75" wide. Would this shape look ok with the slant ceiling? Any opinions?

Shasta-
Thanks for the floor info!

Anyone curious what art over sofa would look like above fireplace? Art's size might look just as good there.