I guess you’re using oh my zsh as your system shell already and would like to use this in the context of the flake, correct?
One nice thing to use is Automatic environment activation with direnv — nix.dev documentation.
What it basically does is: if there is a specific file in the directory it will load the devShell and execute it within your zsh. What you gain is, all things specified as buildInputs (see Difference between buildInputs and packages in mkShell) in your PATH, right at your fingertips in your known shell.