You can install nix side by side to your distro package manager and only install some packages using nix. You could also use something like lorri and direnv and let nix only manage your code projects and when entering the project directory, drop you into a shell with only the dependencies you need for this specific project installed.

Your usecase is what nix-shell is for. It loads an environment on top of yours for just a single project.

guix is similar but can be used on OSes with a traditional package manager. I personally prefer it.