I think in addition to having Electrum on the laptop offline, it can also be necessary to buy a hardware wallet.
If you're willing to learn, consider install and using one of Linux distro (such as Linux Mint) on that offline laptop.
Bitaddress gives 2 public keys: the public key ( 130 characters ) and the compressed public key ( 66 characters ). Are both the master public key ? Which of the 2 public keys do I need to create a watch only wallet ? It’s important not to expose the private key.
In Electrum, you'll just use the Bitcoin Address. Considering it's old, you probably need the one that isn't "Compressed". If you use my test-key from the quote above, it's this address:
1DBZmNMC69PPbC1wjGYaagXQKiba2e5NdS
You won't need the 130 or 66 character hex keys, you'll need the WIF (again: not Compressed):
5KMWmYkn5YWkJnUDG4utD9L1HXQv3DBseqqCGsQXmthcEerbA7k
Personally i would recommend to copy Bitcoin address from compressed and uncompressed public key just to be sure.