Posted: 14/01/2015 at 10:21
Don't buy anything from Parkers. They have a dreadful reputation.
Japanese maples would be fine if you go fo rthe low, hummocky type as they won't get above fence height. I have the more upright Sango Kaku growing in full sun and in a windy position but sheltered by a trellis and it is now 3 metres high - coral red stems in winter, fabulous foliage shape and colour from spring to autumn.
Growing it in a pot would mean you have to be vigilant to keep it fed and watered so the foliage doesn't dry out so get the biggest you can, minimum 80cms I'd say. You can underplant with small daffs such as Thalia or Minnow for early spring interest and a contrats with those red stems.
You coud try a prunus serula which has shiny mahogany bark for winter interest and white blossom in spring but it's prone to diseases and often short lived.
The Italian pencil conifer suggested above would be good in pots but I personally think you need something more rounded to offset your already very angular garden and would echo the suggestion of a choisya Sungold which has evergreen golden foliage and orange smelling white blossom once it's settled and happy. Great contrast too for the black paving and furniture and sunny on a dull day.