Thanks for all the messages. As already said, I didn't have to stay so am very relieved. Danny has gained weight very well since we left hospital, better than at the end of our stay.
There are 3 types of breast pumps.
Manual - I tried one, from Avent, and decided RSI was a serious danger and I wasn't using it.
Battery operated handheld - don't know much more
Electric - I used one at the hospital and found it hard going until Mikey looked into why I seemed to be leaking half the milk all over my skirt and everywhere but in the bottle - I'm also very uneven in flow.
They can be hired via NCT breastpump agents and I have the most expensive kind at £40 a month plus £25 one off payment for personal attachments ie the bits you attach to yourself and which you wouldn't want to share. It sounds a lot but if it works it will be well worth it and if it doesn't I will return it so only the inital £65 will be wasted. Let me know if you need help finding the details - they are on the NCT's website.
The problem is that we haven't yet reestablished our expressing routine since leaving hospital. We sent my dad to collect the pump, and he has kindly signed a direct debit form and refuses to accept payment for the first month and one-off kit from me, though I would have been happy to pay for it having seen how well it can work with effort.
This pump does both sides at once apparently, so if I can get back into it before my supplies dry up, it should be good. Recent expressions at hospital we were managing to get whole feeds and more. I also hope to get in some breastfeeding directly as I do enjoy it when I can get my little monster latched on. But knowing we can at least keep him well on formula if the breastmilk does fail is reassuring.