Update: still struggling a bit, but today stopped using the pump, and found that by hand-expressing I doubled the amount I was getting each time. The pump was uncomfortable even on lowest setting.
Fortunately today I saw a specialist nurse, who was brilliant, really positive, and gave me some good advice, including drinking barley water (stimulates Prolactin production apparently), and reflexology. Other than these, it was mostly common sense, but sometimes you just need someone to spell it out for you.
She mentioned that getting into too rigid a routine can be counterproductive, and it can help to vary it a bit, to give your system a bit of a jolt, and to more closely mimic the variations in times and volumes required to feed a baby.
Other than that she said to keep working at it, and focus on the positives i.e. "any BM I produce is really good for dd", rather than "I'm not producing enough for dd".
I've also had lots of skin-to-skin, and dd has had a few good goes at latching - thought it'd be a struggle to persuade her, but she just did it first time! So I'm sure that will help too.
Thanks again for your replies everyone 