In reply to everyone who kindly took the time to offer suggestions:
Salomon and Haglofs - not much lighter than my current daysac and both a lot fussier.
Alpkit - looks promising, very similar to the Exped. sac. Seems to be currently unavailable.
Black Diamond - looks good. Pity the company is now owned by a pair of See You Next Tuesdays who I would prefer not to support.
OMM - Why had I not thought about them? The Ultra 12 is also a possibility, though again I'd rather it was a little cleaner.
Interested in the comments on the Sea to Summit, especially on the durability. I'll using this on half a dozen routes a year at most, but that is reassuring. Frustratingly, I can't find a EU stockist willing to send the dry daysac to UK.