I've been using Nix for about a decade, and not bothered with flakes yet. However, I also avoid nix-env and channels, as the parent suggests:

- Instead of channels, I use fetchGit with pinned revisions

- Instead of managing installed software via nix-env, I use buildEnv to collect everything I need in a single derivation. If I'm on NixOS I'll put that in systemPackages; or otherwise (e.g. on macOS) I'll use nix-env to only install that one package.

These have the advantage of being declarative files, which can be tracked in git; rather than imperative commands.