Ground cover between bamboo

Snap Nicki, my back garden faces NNE too.
Your garden doesn`t look quite as large as I envisaged, and throws a new light on to it. I`m now not sure why you would consider Heath pearlwort?
At the moment, as the weather is hot and dry with no substantial rainfall expected, it would probably be best to simply plan rather than plant.
The first thing to do is prepare the soil. If yours is dry and sandy it will need lots of good 'beefing up' - rotted horse muck, leaf mould, compost, farmyard manure - spent mushroom compost (a good one, as it is relatively cheap) whatever you can source....
If I were you I would have all that bamboo out again - look after it in its pots somewhere it will behave, and keep it watered (for now)
I can see why you chose the gold colour of the bamboo to make a contrast with the purple leaves there, but you might better achieve the look with other plants (there are loads we could suggest)
The most important thing to remember is that this should be enjoyable - not hard slog. Take your time, get the wine and the lounger out, look at pictures of gardens you like, poke your nose over fences to see what grows well for the neighbours, and stick with us on here...ok

 

PS.. When planning beds and borders, they need to be as wide and deep as possible to work well, so Lord Awful won`t have quite so much grass to see to