I've bought the Maxi Cosi which is the best (ideal actually) fit for it. It clips straight into the adapters, no extra bars and no extra clips or straps required which is the case with other capsules on BJ prams. I'm yet to use my capsule though but everyone I've spoken to raves about them though. I have played with it a bit though, connecting it to my City Elite (I've only just ordered my Select) and it's super easy to connect.

I'm think the Maxi Cosi is only up to 9kg though.