I read somewhere that Princess (and that's the one we want) will take babies on some cruises provided they are six months old. Just phoned them and they said 12 months. Will have to find the info again and call them back to double-check.

Hmmmm, maybe time for a rethink. A resort instead maybe.
If you end up looking at resorts, one of my best friends has just returned from Club Med Bintan and they had a ball. Her kids are older though, 10 and 4, but she said the kids club facilities were amazing along with everything else the resort had to offer. Club Med often do two-for-one deals too and being all inclusive (airfares too if required), there are no nasty surprises on the credit card afterwards, lol. If that sounds like you're kind of holiday, I'd sign up for their newsletters.