Bitwarden is an open source password manager and is super useful. You can store all your passwords and sync on all your devices. You can even some with friends and family as you choose.

Sorry to break it to you but it’s no longer viable to just have 3-4 passwords to memorize or simply add small changes. With the exponential rise in computing power and data breaches, brute-forcing and rainbow tables are increasingly viable.

Just memorize a ridiculously strong password (I recommend a combination of a quote/passphrase and made up words in addition the standard best password practices) and use that for your password manager. Bitwarden and many others have a password generator where you can generate 30+ character passwords