Can you mock up what the mirror and vanity will look like - use some painters tape to indicate where in the room the vanity will end and then outline the various choices of mirror/mirror cabinets. You might be surprised at how some work better than others. With the Kohler Verdera 101cm (40") by 76cm (30") medicine cabinet, it doesn't matter if it's 7" shorter than the sink - what matters is if you are using the sink to wash up, and you look up - are you able to see yourself properly in the mirror? IOW, is it functional.

I'm glad you were able to do it and I do hope it lasts. I don't see, anywhere, how the absolute front of the cabinet structure is supported from weight focused at the front (most likely location), especially if that weight were to be left and right or twist-like challenging the joints (kid dancing or otherwise moving left and right) or up and down (kid jumping up and down). I see no triangles. But if that setup truly works long-term in real life, then you're a better man that me for conjuring it up. You may be able to stand on it when freshly installed, but can you after a couple years? I become concerned then and that's why, with this type of box construction anyway, I wouldn't put my name on that, ever... I mean no offense. Cheap particle board degrades over time with humidity, movement, weight. If we're talking furniture-grade MDF or plywood... okay, I'm more comfortable.

You have to think on the scale of a real-life homeowner, not a designer of high-end homes (unless this is a high-end home!). When things are tight, you look for solutions! If 58" is too tight for two sinks, look at a trench sink - a long skinny sink with a faucet on either end that serves two people. This is the concept, but like so much stuff on Houzz it is marginally useful because whoever posted it just slapped it up without dimensions. In this kind of a get-up, WHERE to center two medicine cabinets becomes the issue, so a single mirror wall does seem to look better. In this example, designer Kelly Gardner does tell us all about her project, which seems only the right thing to do if a designer is getting advertising by posting it here for us to see! She says, " kelley gardner The sink is 34" and the entire width of space is 48". The space between the faucets is roughly 22"Now, doesn't this look like something you could do in your 58" space? Ask your contractor if it is too late for wall-mount faucets (it probably is). Your sink would have 5" more counter on each side. Come to think of it, this may be a shallow counter (maybe they had a space issue) and with a 22" deep counter you may have plenty of room for a faucet. Kelly says that this sink is from Lacava, so if you like this look, review their catalog online, then find a source to buy one. My original bathroom plan was to get a Kohler Brockway sink. Funky, old fashioned and really splash-happy! The Brockway has a backsplash and the whole sink is 18" deep, so in a 22" counter, you can make a little shelf between the backsplash and the wall. The sink has a big round belly that begs to be pulled forward out of the cabinet, and if you do that, you can have a deeper shelf behind the splash. Here are couple of installations.First, this is the smallest Brockway, the 3 ft (36"). It comes in 4ft with two faucets, too. Here, they mounted it against the wall in order to have a bit of counter in front of it, instead of pulling it forward and putting a shelf behind it. Also an excellent choice. This is one of my favorite installations and it also gives you ideas of what you can do with mirrors and cabinets. It is a cottage look, though. This is the "belly exposed" look, where pulling the sink forward gives you room for a shelf behind it. I can't really see a shelf here, but you can see where it would go, where the sink top ends. Just make a shelf behind the sink that fills the space between the sink and the wall. If you have stuff on it, you cannot open the doors of the cabinets here, which is a good reason to leave it off, I suppose! This is the 4 ft model, which is too large for you, giving you only 5" on each side for counter. You should go with the 3 ft, giving you 11" on each side for counter. Wetstyle, from Canada, has many trough sinks. Here are some that sit on top of the counter, just in case the cabinet you ordered cannot take a sunken one.This the the Wetstyle Ove sink in the 48 x 15" size. It is only 4" deep, so you have to be careful to chose a faucet that will not splash the water out. But it gives you rounded corners, lots of space in front or back of it in a 22" deep counter, and you each get 5" on each side to have to set things down. What is even better about this picture is the mirror design. See it? A mirror is inset into the wall cavity, giving you a small ledge to set things on as you are getting ready. It looks like the side mirrors could be small med cabs, if they are not. What a smart design for your small space! Click on the photo to enlarge it and see the details. Click on "More Info" to go to the web page and read what is available about the picture. Here is the Wetstyle Cube collection sink in the same dimension. It is just a rectangular version. Click on "more info" to get a version with the price tags, where you can click on the tag to get a close-up of the sink. Being only 15" front-to-back, there is lots of room for faucets behind it. If you do a shelf in front of a recessed mirror, you may get away with a 4 ft long sink - especially if it gives you space in front or back to set things down. Check out Lacava, Nameeks, and Duravit and you will see many more sinks that sit on top of the counter that are long enough to have two faucets. There may also be some that are "semi-recessed," which means that there is some sink below the counter, too, giving more depth.

just to give you another visual, this is also a 36" floating vanity. 8' ceilings. the mirror is and LED back lit one. there is a ceiling light too. if you wall mount your faucet, you'll have more space and it's easier to clean this was the before similar set up. I like how they did the tile splash and the mirror above it on this one if you could center the faucet and sink, you could do any size mirror you like.