A 12 word seed phrase is secure enough.
A 12 word BIP39 seed phrase provides 128 bits of security and since a private key provides 128 bits of entropy, 12 words are enough.
It may worth mentioning that you can generate a 24 word seed phrase using electrum too. To do so, you need to go to console tab and use the following command.
make_seed(256)
Just note that a seed phrase generated by electrum isn't BIP39. Electrum uses its own algorithm.
How to generate a 24 words seed with a passphrase ? I just tested to select "add words" and put a password when I import a seed but it's impossible to click on next.