This may not be a viable option for you but I'll throw it out there.

Digital voice recorders are very small and they have a lot of storage space. I use one to record my dreams, which I then transcribe to a journal.

There are also private online journal sites and blog sites that you can set to be viewable by you alone. They have an array of features just like a forum or a word-processing program.

For a time, when I was an emotionally abused child, I kept a memo book journal. I wrote in tiny tiny letters to stretch its capacity. I kept it in a place where my mother never found it. If you, the OP, want to know where that was PM me and I will tell you privately.

I understand you have a memory issue. Maybe we (posters) can come up with a method for you to remember where you keep your passwords and journals. Believe me when I say I understand your memory issues. I have them too.