Ubuntu OS is a good system, but it is the #1 choice for beginners and it may not be completely safe if you use it carelessly.
Creating an airgapped wallet is easier. Using tails and an old computer, you will be safe from most vulnerabilities and using your phone to track your balance.
Being secure in terms of privacy is a more difficult choice, and mixers are one of the ways that help you enhance your privacy.
Pass the connection through Tor and send your coins through Coinomize or any mixer and it will be very difficult to track you.
Let me give you an example:
Let's saying you are going somewhere, maybe through customs or something, and your electronics are seized includinh your hard-drive.
Now it just so happens that you used Ubuntu and have done some mixes on that computer and it has your wallet inside.
In such a case, if those coins you put in the mixer have a questionable origin, you are toast.
That's not going to happen however if you use Tails OS or Whonix. Because the wallet and the mixing session will be stored in-memory which will be wiped out on shutdown.