Suppose the following situation: I want a familiar to give me advantage on melee attacks via the help action. However, I do not want to be yet another adventurer with an owl familiar doing fly-by helps. Instead, I pick something smaller (say, a spider), and have it ride on me.
My idea is thus: The familiar, on its turn, readies an action to help me whenever I attack anybody. Seeing as I close to melee to do that, the familiar is within both 5ft of whoever they’re helping and the target, satisfying the range requirement. Is there a RAW reason this shouldn’t work?