Posted: 26/03/2015 at 10:33
Silver birch can grow quite tall, but it has non invasive roots and is light and airy, which is why they can be planted in smallish gardens. I have a silver birch jacquemontii, which isn't huge after 22 years. I think in your garden that 3 might be pushing it a bit, but you can get a multi stemmed one. Photo is my tree in winter.
Crab apples are good for small gardens. So is Amalanchier Lamarkii. Lovely white blossom and autumn colour.