You have found a good solution with KM, but let’s evaluate the possibilites here anyway. It’s interesting to see how we work differently.
For example, I have my most used folders in the sidebar, which is visible in Finder windows as well as all dialogue windows:
Quite often, I have to save documents to places that’s not visible in the sidebar.
Example:
I’m writing a project plan to my client Alltaki and I now want to save it in the appopriate place in my file system. I use the mouse as little as possible because it takes time and effort.
• I press CMD+S to save my work.
• In the save dialogue I press CMD+Shift+O (Same shortcut works in Finder and all dialogue windows) to open my Documents folder.
• In my Documents folder I have two folders; Work and Private.
Note: I think it’s important to have a clear distinction between work and private stuff, and the further up in your hierarchy you can place those distinctions the better for your future sanity. (Many of my clients have their documents in some kind of randomised/chaotic order. Folders may or may not be used, they are scattered at the Desktop, in the download folder, in Mail, and sometimes at the root of the hard drive. My first suggestion is always to use the Documents folder and to create one Work and one Private folder, and they shine up like they have understood something new 
)
Note 2: I always use the Column view, because I think it’s easier to navigate and also to give your brain a descent chance to quickly see where you are.
• I press CTRL+Tab to go to the file area, and then press down arrow. This selects the topmost folder, which is " Clients" (Note the space in front of it to keep it first in the list of items).
I press the right arrow to see Clients, and the list with my clients is shown.
Again, using the arrow keys I navigate to the folder called Alltaki.
• I have a folder called 2023 that I want to place the project plan in. But I don’t have the project folder created yet, since this is the first document for that project.
So I navigate to the folder 2023, and there I press CMD+Shift+N which creates a new folder where I’m currently located.
Then I name my document and press Enter to save it. Done!
To sum it up, I press a series of keyboard shortcuts that have been used for 30+ years (depending on when Apple implemented them) and can navigate, save and open things quite quickly.
But having shortcuts for the most used folders is crucial to be effective, as well as using folders and a thought out hierarchy.
One thing that have destroyed the need of a good hierarchy is Spotlight. It’s so effing quick and good, that many people use that instead of having a good file policy. However, I could not personally live with that. 
/$0.02
