Do you know what an 足軽 is? Ashigaru? If you’ve played any war games set in Japan for example, you might. They’re foot soldiers, so if you can remember what an Ashigaru is, you can remember that Ashi is used for the body part. If not, well, knowing more words always helps me anyway.
Finally, keep in mind Wanikani’s constant refrain that body parts often use kunyomi even in jukugo. So 足軽 and 足元 and 足跡 and 足音 and such that use 足 to mean foot/leg, uses the あし reading. Meanwhile, 満足 and 不足 and the like have to do with the ‘sufficient’ meaning and use そく (sometimes with rendaku)
That’s not an absolute rule though. There are a lot of exceptions to what I just said. But while そく does sometimes refer to legs, I can say I’ve never seen あし in a jukugo that meant something about quantity. I would also say that I don’t usually see そく as the reading of the first character in a jukugo. There are noteable exceptions but it is almost always あし. The opposite isn’t true, though.
Anyway hopefully that can help you with some of the more common words…?