I've been looking at strollers and I think the travel systems where the car seat clicks in seem really convenient. But they appear to only work with infant-only car seats.

Here's where my confusion comes in. Most car seats now are convertible and work from infant size all the way through booster seat size. So to have a travel system, would I have to have an infant only car seat and then also a convertible car seat for when the baby grows or do any of the travel systems work with a convertible car seat?

This stuff is so expensive it seems crazy to have two car seats that safely hold an infant. Am I missing something? First time mom here, please help lol