Using a single private key is not really safe and not good health for your privacy. How about you do it this way.

Instead of creating a seed phrase as suggested above, why don't you create a single seed ( 64 bytes) using the PBKDF2 function (Password Based Key Derivation Function 2). The advantage is that you wouldn't worry about discarding other generated private keys and addresses, You have an additional option to include a passphrase for the safety of your coins against theft of seed.
The difference between a single seed and your private keys is the byte difference, you don't have to worry about handling 12 or 24 seed words/phrase, you don't have to worry about master keys