There is already enough going on in your bathroom.

forget the framed pictures and hang a hand towel ring above the countertop next to electrical outlet. The sconce looks a bit high.

The ideal height for a bathroom mirror is with its center 60 to 65 inches from the floor, positioned 5 to 10 inches above your sink or backsplash. For the sconces, mount them 60 to 66 inches from the floor (center-of-bulb), placed 28 to 40 inches apart to perfectly frame the mirror

Hang pictures at normal viewing height for the average person. Ignore the ceiling height.

I agree with Lyn above. You don’t need much here.

Agree, no art.

I would suggest a wallpaper, though, as the present wall color doesn't relate to anything in the room and it is kinda blah. A texture will make up for no art on the walls. I like this one a lot, as it has all the colors of your bathroom in it. It will work with the silver tone mirror, the marble tiles in the shower (and the black frame around the glass doors), the wood vanity and the sconce and the odd man out brass accents.

Not sure what rules you applied to the mirror but IMO it's way too small for the room. I would have started at the backsplash and made the mirror the same height as the tile in the shower.

Some color is needed. Maybe one right sized piece of artwork over the toilet. Yes, to the suggested towel bar as well.

Also not sure what "rules" you followed and agree that the mirror is too squat/short for the space.

I have 12 ft ceilings and used 48" tall medicine cabinets. If they had sold taller ones, I might have gone with taller ones! Some of my guest bathrooms have hanging framed mirrors and those are 50-54" tall.