In reply to pepperpot:
My experience is that it has to be high summer before they're too hot sitting still in a fleece lined waterproof suit - and even then, they usually need a fleece suit. Things like hats and gloves are good for adjusting the overall temperature. Admittedly we're in Cumbria....
I'd get one their feet poke out of, rather than one with built in feet. It's much, much easier to get them in and out of, and very soon your little one will want to start walking about (holding on to your hands, or possibly even alone - my first was walking at 11 months) and that's much easier in shoes/snowboots/wellies.
And don't forget a sun hat/sunshade just in case the sun appears. You then need to work out a way to get it back on their head every 2 minutes whilst they're on your back in the rucsac!
Togz are another brand worth looking at - more waterproof than many. You'd be surprised how many puddles they can find to crawl in even on a dry day.