create a USB bootable Linux tails os , you'll need two drives for the installation process, only one of them will be your bootable drive (other one has some intermediate installation data)
os is really secure, even basic commands like sudo, make, apt-get are disabled by default for security. Extremely difficult to install shit, and you wouldn't want to tweak settings to make installation possible as it's not recommended if security and privacy is your main goal
electrum Wallet is present by default, although you might need to update (run latest version from source)
keep the wallet in "persistent" folder if you want to save the files for next reboot , everything else outside this folder is stored in the ram, and gets erased after powering off
create wallet while offline , you can type the private key seed on a .txt, right click, encrypt it with a passphrase (uses pgp encryption) and send it to yourself
While some may argue saving your private key digitally is risky, and that paper is the way to go, but I don't see any way someone can steal your keys if you do it like this. You just have to trust that there are no hardware keyloggers on your machine, or a compromised firmware - both extremely unlikely
you can use my ether wallet offline and do the same for ETH
when you want to see the private key, you can either log in to a tails session, or even decrypt it on windows using CMD (this doesn't create any file with your private key, just displays it in the cmd ; making it pretty safe, although less safer than using tails to view the keys - you could still be screencapped or something by a good enough s/w keylogger)
use this command for decryption :
gpg --batch --passphrase-fd 0 --armor --decrypt filename.pgp
This setup is like building your own hardware wallet, almost as good as ledger or trezor. ALMOST . PS: I'm still getting a Ledger !