Supposedly gods of destructions and angels can use ultra instinct, but they dont get the aura and eye colors Goku gets. Why is that? Is Goku using something else in this transformation, such a super saiyan transformation on top of it, god ki or something?
The biggest thing is that Ultra Instinct is not a power up, but a technique. It is literally just your arms and legs thinking for themselves, defending without you needing to be involved. There is no transformation or power up associated with it. It's implied that mastery of this technique means being able to have it always active. Whis talks about how his feet think for themselves but not his shoes when he stepped in poo, implying that it was active at the time, but since he cant feel through his shoes, his feet couldn't think to avoid it the instant he came into contact with it to prevent stepping in it.
Goku's transformation was triggered by the Spirit bomb, and he reached a new level. This is the new form he obtained. While in this form, he had, as Whis put it, broken through his shell to the greater potential within him. It was by breaking through to that new form that he was able to use Ultra Instinct. Its unlikely, but possible that Goku can still use Ultra Instinct even now in his base form. It could be the same principle as with his god form in his first fight against Beerus, how just obtaining it made his base form a lot stronger.
Or, TL;DR, Goku obtained a new God like form, and while in that form, was able to comprehend the secret to using Ultra Instinct. They are separate things.