towheedm's suggestion to use Debian Stable is a good one. A distro cannot get any more Debian-based than that.
It is unlikely packages would be a problem, since Debian has more packages than Ubuntu, and most of Ubuntu's packages are Debian packages modified to run on Ubuntu.
Keep in mind that Debian can be more difficult to set-up if your computer has hardware that requires non-free firmware. A small issue, but one to keep in mind.
And if you find Debian too difficult, there is Saline, which is basically Debian with non-free firmware and a few other goodies pre-installed.