You can request a sample of the Convatec Moldable wafers...no cutting or measuring and they work with odd shaped stomas!
It's just like with anything new in life...it takes time to get used to and adjust things.
It's actually a good thing that your stoma points down, too
Have you tried the marshmallow trick? Eat one or two about
15 minutes before you change and it should slow things down so you can change your appliance when it works for your schedule.