K.K.
Hi! If you could give me some more information, I can do some research for you and give you some seat names. I know from what I've read the combo seats aren't always a cheaper way to go b/c most kids outgrow the car seat portion before they are old/big enough for the booster seat. You said you have a 3yo who is 36 lbs...is this weight with clothes on? Also, how tall is her torso (easiest to measure when she is sitting on her bottom against a wall or door jam and making a mark at the top of her head). Even though car seats go by height and weight, not all children's heights are equal (a child with really long legs and a short torso will be able to be in a seat longer than another child of the same height with a long torso and short legs). Also, what price range are you looking for? Sorry for all the questions, but I'm a big car seat advocate and would love for all children to be as safe as possible while in the car (the MOST dangerous place we put our children on a daily basis).
K.