How to disable ufw on boot?
You can indeed stop the service with your command, but obviously it will be restarted next time. What you need to do, instead, is disable the service that starts ufw during the boot process of the computer.
sudo systemctl disable ufw.service
If you want to restore the service, substitute disable by enable in this command.
If you never want to hear about ufw again on that system, you also can completely remove it from your system: that will remove the systemd service and the program.
sudo apt purge ufw