Oh and sorry Kathryn, just re read your post..  They aren't cheap, so if were you, would just buy a good quality inlay to craddle the baby (at one end, its shaped like a half circle if that makes sense) or a nice sheepskin rug.  You could make it super cosy in there.
No need to splash out on the sun covers, for ages I just used a fine cotton muslin cloth and pinned it on with pegs..  And ask yourself - how often will I go for a walk in the rain..??  If it's pouring with rain, me and the kids don't go out, if it's drizzling or I have to go, I just do my best to get a covered carpark..  A brolly or a muslin cloth will be fine if raining and quickly dashing from shop to shop.
Hope that helps..  Lastly, if want a rain cover, get a double one if you're thinking of having more than one.