What seat to get toddler once infant outgrows the infant carrier?

[Amy]

I appreciate all the feedback these boards have provided, but I am conflicted with what to buy next. I am due to have a baby in 3 weeks. The newborn will go into the infant seat for lets say 8 months (that how long my son lasted) at which point, the baby will be moved into a FPSE (toddler is currently using). My son is almost 2.5yrs (born 9/00) and is approx. 37-38lbs and 37". I am not sure how long it will be before he hits 40lbs. He definitely has not been gaining like he use to. So should I wait it out and see when he hits 40lbs and then get a new seat or should I invest in something like the Marathon now? I think the Husky will be too big for our backseat. If he made it until he was 3 should I just go with a BPB or should I still look for the higher weight harness system?

Any feedback would be appreciated.

Thanks