Re: my carseats expiring
Depends on how much money I was in the mood to spend, how fancy I wanted the car seat, how picky I was on color... and the vehicle.
In my state, children must be 40 lbs to ride in a booster, so that narrows it down to harnessed seats only.
On the low end, I'd get an Evenflo Maestro. It's quite inexpensive and will do the job nicely.
If I wanted a cushier car seat for more money, I'd get the Britax Frontier 85. A child that small certainly doesn't need the high capacity (assuming no special needs that would require him to be in a harness until age 12 or something), but I do like the Frontier.