I do something similar (though less secure) for general purpose passwords; I have a couple of common “base” passwords that are decently secure that I commit to memory. Then for each website/service, I pick a pattern based on the name/url (maybe something like the first two and last three characters of the url), and append them to one of my “base” passwords, so each site gets a unique password, but I only have to remember a couple of them + the pattern