I was going to order the Britax Companion, but I may just get the Britax Marathon and wait and see. Since we're having a homebirth, if baby is smaller than we expect, we can go out and get a bucket seat quickly at Target.
But I really think baby will be 9-11 pounds. I would be surprised if it's only 8 pounds or less! At 9-11 pounds, the Marathon should be just fine. Should I have to buy a cheaper bucket seat, we'll deal with that. But I like that the Marathon goes to 65 pounds, so one seat is all we need.
**** YOU SHOULD NOTE ****
If you buy a Britax, you should buy it early and let it off-gas for a few months. They're one of the more toxic ones, but are also a GREAT seat. So by giving time for off-gassing and maybe washing the cover, I feel confident I am picking a good seat.