I would agree about holding off on the purchase of a convertible seat - or really any seat for that matter - until closer to your due date. But not *too close*!! I'd recommend around Valentine's Day... then you have it in case the baby comes early, have time to get it installed and learn how it works.
As far as recommendations, if you could let us know what vehicle you will be putting it in (year, make, model) that can help as some bucket seats just don't work in some cars. But my personal recommendation would be to stay away from Evenflo seats as they require the handle to be down plus clearance and that eats up a TON of room in a vehicle.
As PP said, you can use a convertible seat for an infant, but I know I sure liked the ability to take baby out of the car when she'd fallen asleep, so I do think there is value there. The travel system seats tend to be just fine: you can always move into the convertible after 3-4 months so it's not a big deal if they only go to 22lbs and they tend to be more affordable.
Good luck & congrats!!
Melissa