I know this is completely out of left field...and possibly insane...but I just had a thought (always a dangerous thing).
What about Gary Oldman as Bilbo Baggins????
I know he is usually cast as some insane baddie, and not the typical choice.
However, if you look at his face, there can be a kind of earnest simplicity to it. And he looks short!

I could just imagine him sitting in the twilight outside Bag End, puffing his pipe.