Set a git commit message in bash but also go to Vim for further editing

A colleague insists that messages abide by the 72 character limit advisory, and i want to change my habit to get the files-changed and, just as important, files-left-out information that git commit will give in the Vim editor.

I'm still a bit addicted to the git commit -m "Message here" workflow of entering messages right in the command line, and it's more than just habit: it is very useful to be able to look at the git add -p record.

In short what i want to do is both git commit -m and git commit. This may be very inelegant, happy to know a better approach with bash or git, but adding these lines to .bashrc does work:

# Commit and leave a one-line message.
gcm() {
  git commit -m "$1"; git commit --amend
}