Regarding Kant's philosophy more generally, I acknowledge that it is a substantial piece of work deserving of close attention. Nevertheless, I don't like what I know of it. Yes, we do need 'form', but only if we stretch the word 'form' to cover the limiting form of formlessness. Sorry to seem paradoxical. Let me try to clarify this in set-theoretic terms.
Some people say they see things in three spatial dimensions.
Therefore, we can conceive of, say, a recently born baby who has not yet built up that mental infrastructure of spatial relations. His 'visual' sense data are a disordered set. Well, if we wanted to be pedantic, we could say that the unordered set is a 'form', but it would be truer to the normal usage to say that it is the absence of any form. Form is dispensable. Although Berkeley did not explicity discuss this at a theoretical level, his comments on the Molyneux problem suggest that he would concur with what I am suggesting here.