Btw, is it possible to convert a Bip39 seed phrase into an Electrum seed and vice versa?
No, Electrum and BIP39 represent two separate mnemonic standards. It's not feasible to input a BIP39 seed phrase into a function to generate an Electrum seed phrase that generates the exact same addresses from the BIP39 seed phrase.
I'd opt for Electrum. Since it's widely used for storing bitcoin by many, it's extremely likely that it will remain accessible in the future.