Unfortunately, digits and disc base games are separate purchases. There is no ability to trade between them.
Based on your notes history, I'm guessing you never purchased The Taken King? If so then yes, your best purchase would be Destiny the Collection.
Characters are attached to your console account - sign in with the same Xbox Live Id and your characters will be there.
As long as you haven't changed console generations, your licenses for CE content will also still be available.
Thanks for fast feedback. This is what I thought. Just didn't want to buy it all to see progress wiped and collectibles lost. Playing on same original console.