Where are you planning to put the mantel? IMO just above the tile is too short so add some tile to bring the surround up to proper mantel height .It should be about 48-52" from the floor . Iam only guess the height of the tile now. I sure hope no TV above that mantel either . As for size I like them to be the same width as the FP surround.

could we get some perspective w/that entire wall/space? have no idea without seeing everything

why didn't you go a bit higher w/the tile?

if that is a wood burning fireplace, code requires a certain clearance when using a mantle above the firebox

I think it's about 30-36" or so.

Is this what you had in mind? (these are electric, hence the lower mantles)

or do you want this style?

Here is the whole wall

The tile surround is 43.5” high

It’s a gas insert
We are putting a tv above it

I added more pics to my last comment.

what about this look?

That’s super helpful thank you!

Or, any of these (Lots of ways to do it)