Natives are the best plan I think. The wild roses are great as they flower well and are spikey enough, but they look pretty rubbish in winter even if the hips stay on. I have masses of them and would be happy to send you some bare rooted for postage money if you PM me.

Dogwood is another good choice. Looks good all year, is a doddle to just chop back when you fancy, nature loves it but doesn't live in it (rats + banks + many plants = disaster!) and it has so many types. I bought three each of red, yellow and albus and they layer so well we are selling them in dozens now!

What about some Hebes dotted in here and there? The larger ones are nice all year. Ours are in flower from mid summer until now even in this Northern windswept area. If you're on acid soil, rhodies may be good, too.

Enjoy the planting!