Yeah, those pictures with the line where the wall is under neath really do help.... you're in deep doo-doo! :laughing:
Just kidding.
But as others have mentioned, you're going to end up having to remove the decking and make a solid floor (or roof, depending how you look at it), and then put the deck back.
Or, as you mentioned, get that manufactured interlocking decking, but it will change the look of the deck a lot with the boars running perpendicular to the house. Not saying it will look bad... just look different than you're used to.