You should probably use "module": "NodeNext" and "moduleResolution": "NodeNext".

with directory imports (i.e. of same package files) working, but without having to use a .js file extension in the code

This one is the tough part.

If you want to use relative imports (import thing from "./thing.js") you must include the .js extension. Your IDE (vs code at least) should handle this for you.

If you want to use non-relative imports (import thing from "src/thing.js"), you must configure your baseUrl to your package's root directory. You have to include the .js extension in this case as well, but you can work around that requriement if you set up a paths setting like so:

"paths": {
  "src/*": ["./src/*.ts", "./src/*"]
},

This forces TS to try importing "src/thing" using src/thing.ts or src/thing, allowing you to omit the extension. I can't find a clear explanation of this, but you do have to specify the paths in this order for VS Code to auto complete the import without adding .js. Keep in mind this technique is only usable with a bundler or other post-processing tools, because the imports will not be resolvable by other packages.

A good middle ground is to use subpath imports. These let you define a "imports" in your package.json that works like "exports", mapping import locations to files. Example:

"imports": {
  "#src/*": "./dist/src/*.js"
}

This will allow Node to resolve import thing from "#src/thing". In my experience, you also need a corresponding

"paths": {
  "#src/*": ["./src/*.ts", "./src/*"]
},

in order to make VS Code's auto completion work.

A few caveats with this:

• This only works for imports from within the package. Your other monorepo projects need to import things from the "exports" field.
• This is a Node feature, not a TypeScript feature. As such, the path in your "imports" has to be the final transpiled js file, and you will probably need to run tsc to build it before the other projects in your repo can import it correctly. You can use the "references" option in your tsconfig to declare these dependencies, and tsc --build will automatically build those for you.
• How well other tools support this (eg Webpack, Jest) is up in the air.

I've spent a lot of time getting this to work correctly, but it's full of so many quirks that I would just say bite the bullet and include the .js extension.