Hi Aquagility,
Sounds like some low-growing creeping evergreens should fit the bill, which will also take a fair degree of shade.
Some that I find that work well are -
Vinca Minor (Perrywinkle)
Berginia (Elephants Ear)
Pachysandra
Ajuga Reptans (Bugle)
Symphytum (comfrey)
The last one is very good but is best planted on it's own, as it does like to take over. if you find it too invasive it can easily be dug up and will not persist though.
Plant them a little closer than recomended and you will soon find they will fill in the gaps, planting in groups of 5 or 7 looks more natural.
Good Luck Googling Tbird+