One of the biggest upgrades from using fish is syntax highlighting / autocompletion. You can get fish-style syntax highlighting and autocomplete in zsh (which has the advantage of being more interoperable with bash generally):
In combination with all of the above, [fzf](https://github.com/junegunn/fzf) suddenly becomes a syntax-highlighter preview-pane via leveraging bat (or delta, as the case may be).
[zsh-syntax-highlighting](https://github.com/zsh-users/zsh-syntax-highlighting)
[zsh-autosuggestions](https://github.com/zsh-users/zsh-autosuggestions)
Poster mentioned "modern alternatives exist" with good colorization options. Some of my favorite colorized feature-rich alternatives:
ls -> [exa](https://github.com/ogham/exa)
cat -> [bat](https://github.com/sharkdp/bat)
du -> [ncdu](https://dev.yorhel.nl/ncdu)
diff -> [delta](https://github.com/dandavison/delta)
In combination with all of the above, [fzf](https://github.com/junegunn/fzf) suddenly becomes a syntax-highlighter preview-pane via leveraging bat (or delta, as the case may be).