this is what I did for my mother in law with a similar type garden. got rid of all the grass then made a small shrub bed(put down weed preventer sheet first) then planted up lots of tubs of flowers they can be moved around till you get best effect, try wallflowers, sweet william, stocks, poppies all can be grown from seeds, be sure to have a pot of NIGHT scented stocks near your door the perfume is great at night time.(a packet of seeds grow quickly and go a long way)
You might like to get a small trellis and plant sweet pea up your wall, also if you have any sunny spot in garden with a seat get a cheap arch and plant a few climbing roses, enjoy.