Look at Piet Oudolf. Lots of ideas for dry gardens. You can then Intersperse with wildflower seed, or plants such as Astrantia, Circium, Bergamont, valerian, Aqueliga, California Poppies, cornflowers and nasturtium. These are easy no nonsense plants, which mean no weeding and loved by bees. Also I suggest looking at Jekka Herbs, for really excellent plants.
Would the bog garden trick of burying sheets of plastic (punched through with a garden fork for drainage) work to retain a bit of moisture? Old compost sacks are ideal.
This might allow sufficient moisture for evergreen ericaceous, giving structure/ habitat/ year round interest towards the back of your cottage garden plants.
Just thinking out loud, I'm still a novice
I have various mini log piles in the bed surrounding my small wildlife pond. You can't really see them amongst the planting but they provide valuable habitat and retain a bit of moisture (my bed is SW facing and gets a lot of sun).
I think I'm going to add bark chippings or this stuff this year as the soil gets baked in high summer: