Paste this into Terminal. It installs sylvie for your user only and switches to it right away. It doesn't need an admin password or a logout. If macOS asks whether to allow osascript to enable an input source, click Allow. Remove it when you're done on a shared computer.
curl -fsSL https://crtep.com/sylvie.sh | sh
curl -fsSL https://crtep.com/sylvie.sh | sh -s remove
Or download sylvie.keylayout and put it in ~/Library/Keyboard Layouts.
Sylvie is based on Handsdown.