Thanks for the replies so far.
Kuoni and H & J only seem to do the cruise as part of an organised tour of China, but I've emailed them to ask if you can do the cruise on its own.
I did look at China Holidays before, but the only beach resort they seem to go to is Hainan and I've been a bit put off that after reading some recent reviews.
Oh well, I'll keep looking. It's not going to be for at least 2 years yet anyway, because we've already booked 3 weeks in Paxos for next year, so I've not got many days' leave left before April 2009. I just like planning in advance - it's half the fun
Elaine