Convertible Carseats for Compact Cars?

Ok, so I don't even have a compact car, not at all, but because my husband is 6'2 and or some reason when they designed the Dodge Journey they didn't think anyone would ever need to put carseats in the back, we have to buy the most compact car seats available.
We went through hell and back before our boys were born trying to find carseats (infant carriers seats with bases) that would fit and even once we decided we'd HAVE to put one seat in the middle, and one behind the passenger seat (with my seat up further than I'd choose), we made it work with Chicco Keyfit. However, my boys are one now, and not anywhere near the 35lb weight limit (do people really carry 35lb babies around in infant seats anyway?!) but I feel it's time to move up to convertible car seats and I have NO idea where to begin shopping, what brands, models, etc. We're going to HAVE to try fitting them in our car before committing to any and there's no Babies R' Us, or really good baby stores in our town so we'd have to drive a little ways to get to a store with a good variety to try.  So does anyone have any suggestions? Keep in mind they have to be side by side, one in the middle of the car, one behind the front passenger seat.
And I can NOT afford to get the top of the line as we're living on a single income. And do most of you buy four (two for each car) and haul them back and forth between cars?) I ask because we use both cars equally when traveling with the munchkins.

Thanks in advance!