In short, use the template on ACC Drive.
If you want an "approved" heraldic badge then you probably need to get it properly designed by a specialist. I don't know if you will end up with a usable vector image at the end of it but it will be formal.
If you just want to go it alone and maintain control, do your own thing but ensure it is appropriate. Maybe run the draft past your wing before too much work goes into it.
Finally, they aren't squadron crests, they are squadron badges. A crest is something that sits atop a helm on a coat of arms.