Online security is not easy. There's always a struggle between effectiveness and ease-of-use; if it's too easy to use, it's probably not effective (and if it's too hard to use, it won't get used -- or it will be weakened when people use the same password for every account they have).
Passphrases are a good way to secure your bank accounts, and they're pretty easy to use. Instead of using a traditional password, you use a set of words. Passphrases have more characters than plain-old passwords, and they're hard to guess.
Researchers have found that it's best to build your passphrase out of words that are not commonly found together:
"According to a new Cambridge study, a common phrase, like, say, "outofthepark," is only marginally more secure than a dictionary word, and anyone looking to crack your password already knows to try common phrases along with common words."
It's not difficult to build a secure (and easy to remember) passphrase. Lifehacker explains how to do this, and commenters on the page explain how to deal with difficult requirements (like short passwords and a requirement to use certain characters or numbers).