A few more photos of the entire bathroom would be helpful.

What is the finish on the bathroom fixtures?

How wide is the vanity with counter?

The existing sconce placement looks high but it might be crowded if you move them lower to be on either side of a mirror. Have you considered an over-the-mirror light? Are there any walls studs that would prevent this type of fixture from being centered over a mirror?

Are you looking for a flat mirror or a cabinet mirror with storage? Consider:

Mirrors with shapes:

Backlit mirror, no sconces needed:

Pivot mirror:

Rectangular mirrors:

Sconces should be mounted around 60-65” from the floor for the best lighting. If you’re limited on horizontal space, you can have mirror cut at a glass company so the sconce can be mounted on the mirror. It will also increase the light. Or you could net a slightly narrower tube sconce. What style would you say your bathroom is?