New carseats for 2004 Chevy Venture

[5kids]

We were in an accident and need to replace all our carseats. We have to fit 3 across in the back of my 2004 Chevy Venture - 8 1/2 yr old (4'9", 70 lbs) rides in adult belt, 6 1/2 yr old (4'2", 55 lb) rides backless booster, 3 1/2 yr old (42", 40 lb). The problem is we don't have a shoulder belt in the middle, so the 3 1/2 yr old must be in a 5 point harness rather than a booster. So, I need a carseat (preferably that converts to a booster) with a high weight limit that is also narrow enough to avoid squashing the oldest. Is there such a thing?

	Booster Seat A booster seat raises your child up so that the car's lap and shoulder belts fit correctly. The lap belt should fall across the upper thighs. The shoulder belt should go across the middle of the shoulder and chest. A booster seat is used for older children up to about 80 pounds. Some states have passed laws requiring booster seats for children up to age 8 or 80 pounds. Check your state's law.