Look at diceware.com for a good way to do that. You can calculate the entropy without "research". I use a simple python script for the purpose, filtering out the words < 7 chars long from /usr/share/dict/words instead of bothering with the official diceware list. Example output: "snored-Hoff-virtue-tab-eroded-Perl's" with estimated 87 bits of entropy. If you write the phrase on a piece of paper and refer to the paper when typing the phrase into a computer, then after a few uses you will remember the phrase without any special memorization effort. At that point you can shred or burn the paper, or possibly record it in an offline encrypted file requiring its own security efforts.