Alot depends on what you need to store.

Could you find or make a tiny slim cart or rollout shelves to put between that storage tower and the vanity. Could you add a small wall cabinet above the toilet.? I have seen shelves between studs hidden with picture frame doors. Back of the door racks and towel hooks are great storage. Hide extra toilet paper in pretty basket on shelf above the door. Bolt decorative tins or basket to the side of that tower to hold small toiletries. You might find creative ways to store more things without a new vanity.

Get a sink with a smaller bowl and more counter space. Then go as wide as possible with the vanity. Can you tweak the storage tower on the left? You have teeny tiny baskets on the shelves. And put shelves or a storage cabinet over the toilet.

Since your width is restricted, you can custom build a cabinet to run the length of the wall, but still stay as shallow as it needs to be, and add a countertop with a sink that juts out as you have it. May be expensive or hard to find a sink/counter like that though.

I would keep the vanity and sink as they are, and custom build a new tall cabinet the same shallow depth to replace your unit in the corner. Run it floor to ceiling for storage, and put the door hinges on the wall side so you can open it when standing at the sink.

I agree that your best solution is custom cabinetry so hat it can be narrow as you need as well as run the length if the wall. Maximize the functionality of the cabinet by installing rollout under the sink and rollouts In the talk cabinet.

If possible use the mirrors as some form of medicine cabinet. These can actually also be custom and built in. My medicine cabinet was made by my cabinet maker but I have seen medicine cabinets that are mounted above the counter with a lot of storage.

more ideas:

if you can swing custom cabinets, you'll be able to maximize every inch of that space. sliding doors could be a good idea for your situation. I've never seen that in a bathroom cabinet, but it could work.

I don't love vessel sinks, but they are a space saver (since it buys you more cabinet space underneath).

don't limit yourself to just bathroom cabinets. find the perfect vintage buffet that fits the space? get a piece of quartz cut, and have somebody handy to help you install a vessel sink on top.

Lots of good suggestions here, but what's your budget? A photo of the whole space, and an idea of how long you want the vanity to be, would also be helpful You said you want something longer, but how long? I assume you still need room to hang your towels to the right of the vanity? Do you want to get rid of the tall standing unit that you have, or do you mean that you don't want a second one?

Not a pro. As others have said, a custom vanity would be an ideal option. However, here are some non-custom options from the Houzz site that might work for you.

40" Larch Canapa Bathroom Vanity Set · More Info

33" Glossy White and Larch Canapa Bathroom Vanity Set · More Info

Look into over the door storage. You might find something useful.

I hate those protruding sinks....they take up too much space for so little storage. I would get an 18” deep vanity with a normal-size one-piece sink and counter. Try to get a vanity about the width of your mirror. A wide sink just takes away from available counter space.
Store towels under the sink and keep your stuff in the wall cabinet in baskets or boxes which you can put on the counter while using your stuff. Your mirror looks good and can be reused.

If you like modern style, Nameeks (from Italy) makes a number of sinks in counters that are 17" deep. They do also make some vanities, but I don't know what you will find elsewhere on their site for matching vanities. Here are the 17" deep tops. You set them on top of a wall-hung vanity, have a vanity made to fit, or you can just get the console stand that many are shown with. The stands might be best since you don't want drawers.

Nameeks Scarabeo 5123

This sink with integral counter comes with the sink centered as in this photo, or off to either side, giving you one larger counter spot.

Cabinet above the toilet can also provide additional storage. Re-train your household to keep the toilet lid cover DOWN so items don’t fall in.

Have a woodworker create bookcase-like shelving INTO the wall between the studs.

Looks like you have tons of space available. The little shelf to the left of the vanity can become a small closet. Any handyman can do that for you. Above the vanity, you can put a medicine cabinet as big as the vanity. Many vanities are sold with a matching medicine cabinet.

Ikea now makes their Godmorgan vanity in a shallower size.

Thank you everyone for your suggestions. If I wasn’t clear I’m trying to get rid of the tall standing unit, I feel it looks cheap and it’s taking up extra space. What I was hoping for is a longer countertop, with storage space underneath. Unfortunately we can’t take the standard small 18 inches as it would restrict space on getting to the toilet. I will look into getting a custom long cabinet. Although this might be out of my budget. Thank you for everyone’s help!

How long a vanity do you want? How about using upper kitchen cabinets as your lowers for the narrow part? They're shallow and about the right height. Ikea are 15" deep and 30" high. It's like the first hack in this link. Ikea also has 15" deep base cabinets for kitchen and bath https://www.housebeautiful.com/home-remodeling/diy-projects/g2776/ikea-cabinet-hacks/?slide=1

kateygaydon - from the responses, I think everyone knew that you were trying to get rid of the tall standing unit. I'd go with a deeper vanity since there appears to be a bit of space and replace the tall standing unit with another unit with doors....Along with the overdoor storage....Good Luck!