Something that would do well in the NW.

The nursery sold me some Rhododendrons that are supposed to tolerate low sunlight about ten years ago but they're finally dying (along with my patience).

They started out OK but the big Maple they're under has doubled in size so sunlight is almost zero this time of the year.

Fern's maybe?

Ferns should do well, if you help them wet.
Not a shrub, but hostas are shade loving. There are varieties that get six inches tall and others that get two feet or so.