How far along are they? If it's still in the early stages you might be able to get a change order. Yes, ask for them to change based on the upgrade being the same price. If it's nearly done you will have a smaller chance of getting what you want vs. if it's early.

@HKO HKO, thanks! That second photo (with mirror shelf) is one I've been eyeing for several months! I initially intended to copy that look...until it dawned on me I don't have an alcove vanity! lol Re going without a backsplash, that is something I've pondered. Unlike our resident River Otter, my husband and I know how to keep water in the sink! :-D Sometimes I have to catch myself when I realize I might be considering a certain style only because "everyone" on Houzz/IG does it (or seems to). The skinny mirror look woke me up to that. I'm definitely aiming for a simple, streamlined look and, to me, that seems to work best by keeping vertical surfaces streamlined as well.

I recently remodeled and changed the double sinks for one sink plus a nice area where I can sit down for my ablutions. I wanted the increased counter space as well as the increased storage space. I don't spend that much time over a sink anyway so I don't see what the big deal is to have one sink. I especially think it is ridiculous when I see two sinks crammed into a small vanity with a tiny bit of counter space - so big deal you have a dysfunctional bathroom space but you have two sinks. I remodeled for my needs and my aesthetic vision. I am not planning to move and if someone doesn't like it, they can fairly easily just reconnect the plumbing and add the second sink. In terms of mirror treatment, I did a ceiling to counter wall to wall mirror but then put two different mirror treatments above the sink and the "grooming area". The wall to wall mirrors lightens and enlarges my rather small space and the two different mirror treatments differentiate it as well. I also have two Art Deco style sconces above the sink and a version a makeup lighting above the grooming sit down area.

I'm going to agree with two mirrors, and add something that goes against conventional wisdom: I think that two smaller mirrors make the space look larger than one large mirror. The breathing room - wall space - between the mirrors makes the space look less crowded & more open.