
This is tricky because I coundn't find one that actually fitted my Cannondale Jeckyl. Because of the suspension unless you can switch it of it becomes a tad unwieldy! I gave up and went for an Adam's trail-a-long (c£100) with a back rest (£10) to strap in a sleeping child. It can also be adapted to hold any child seat by bolting directly onto a seat post. The advantage of a trail-a-long is that you can do all your usual rides and swap with her indoors.
This isn't as good as a Burley trailer for tiny infants but it did the trick for me. I have seen a more recent child seat design which did look more logical for a full susser - I'll see if I can track it down on the web.