Some sort of wall sculpture or collection of pieces. You can put almost anything that is relative flat on the wall if you have a reliable way to attach it.

Sizable dark wood carved pieces come to mind.

a Large sculpted 3D piece like a bird?

there is already a lot going on, so it doesn't need much. If you want some kind of print, I don't love how there's glass over the current artwork. Consider stretched canvas -- a painting or a print. Framed or unframed, just no glass.

Your furniture looks modern, so look at West Elm, Crate and Barrel, Room and Board, etc, for art.

Scale is important! When shopping for art, note the size, and then mark it out with tape on your FP so you can be sure it's big enough.

Not sure if I got the scale correct on these mockups below. If you find something you like, tell us the measurements of the FP and we can help create accurate mockups for you.

West Elm:

I actually like your art there (Texas here, we love our Bluebonnets), but would frame it with non-glare glass. The colors look really pretty and the size is great.

For the mantle, I’d just find things you’d like to display … don’t worry too much about size. If you put large things there, it will overpower the rest of the room.

Beautiful fireplace, and home. It’s a wonderful focal point.

On my floor to ceiling stone fp, I hung a very special-to-me picture, and display glass balls I’ve collected over the years.

With such strong stone, and beloved art, simplicity can be a nice juxtaposition on the mantle.

I just wouldn’t scatter things about, rather do one piece of something to display or a grouping. Interesting candlestick holders, a collection of something, pottery … so many options.

I think this is one fireplace that shouldn't have anything on it.

A few small items on the mantel (?) like you have are fine but no hanging art.