src layout _should_ work. The pyproject.toml needs to live next to src, not inside of it. You might need to `uv run python` in order to pick up the right PYTHONPATH?

https://docs.astral.sh/uv/concepts/projects/init/#packaged-a...

    uv init --package example-pkg
    cd example-pkg
    uv run python
    >>> from example_pkg import main