I thought it was about time I gave an update since it's nearly a fortnight since my last (first) post.
Many thanks to those who commented with ripple pattern suggestions, especially jess (who hopefully will read this as I don't know how else to reply to your comments). I read all the comments, followed some of your links, found a few other places to look. Then it was time to leave the house to road trip to chorus concerts and my husband had decided to back up his hard drive which meant I couldn't actually print anything to bring with me and had no time left to copy things down.
Not to be deterred I read through jess's comment again which explained the mechanics of rippling (I knew I should be able to work that out for myself but just hadn't been able to by myself). Then I collected up my yarn and hooks and once the baby was asleep made some swatches.
I didn't like the first attempt so much because of the holes and it didn't ripple in quite the way I was looking for. So I tried again and came up with a ripple I like. I believe it's actually almost the same as jess's improvised pattern except that I'm only doing dcs in 3 stitches between increases and decreases instead of 6.
Then I had to decide what size to make. I've taken the in-for-a-penny in-for-a-pound approach and decided to make a blanket big enough for our queen size bed (we could use more big blankets).
So I've been slowly working on the blanket for just over a week. I've been carrying it around with me and snatching a few moments to crochet where I can. In the car, reading at computer/watching TV, sitting on the floor/ground next to the baby when she's playing happily, sitting outside in the sunshine with baby napping in the stroller (my personal favourite).
I can't move too fast since I need to get more yarn. There are two more colours to introduce that I have on hand (a pale blue and a darker purple) but I also want to get a pale yellow and perhaps another blue too. I think I'm going to get a dark brown to edge the whole thing when it's done but am undecided about whether to get any brown for in amongst the ripples too. Either way I certainly will need to get more yarn soon.
I'm pretty pleased with the way the ripples are looking. I'm thinking that I should start using the random stripe generator others have mentioned since I'm otherwise liable to over think colour placement (which rather takes the joy out of it) or just repeat this first sequence over and over (which I don't want to do, I'd rather have it be a bit random even if I'm not using a big variety of colours).