In reply to Gall:
A lot depends on the overall area available to you for plants.
Ideally bushes, hedges or shrubs, somewhere the birds can take some refuge in, also plants that attract insects, like bees, butterflies might help.
For small trees, consider juniper firs which can be bought in tubs, you may be able to build a raised flower bed, and plant things like lavender and erysimum.
The link below will take you to a photo of one such raised flower bed that was cleared out and replanted back in May 2020. The overall length is a little over 2.5 mtrs L x 0.5 mtrs W and approx 30-38 cms deep, to give you some idea. You may even be able to buy a raised flower bed, have a look around at what is available.
https://www.flickr.com/photos/peak-rambler/49904791403/in/album-72157714135351448/
Mike
Flickr Peak Rambler