Radian 3RX

We have a travel car seat - the diono r3 - and you can buy straps for it that effectively make it into a backpack. We've used it domestically and internationally and it fits on coach seats (front facing) and then you can use it rear facing for the car once you get where you're going. Every time we travel with it, we have parents stopping us and asking about it. Super light weight and easy to use!

We loved our Britax Boulevard but it was not at all good for bigger kids rear facing longer! I think the weight limit was 35 on latch install which some of my kids hit before age 2. We had to change to Diono Radian and Graco Extend to fit to keep them rear facing.

I’d recommend 3x of the diono seats. Their whole marketing thing was that you can fit 3 across in most cars. I found them easy to take apart to clean as well, although maybe that was because we just had so many and we did it a lot of times it got easy. On our last trip which had like a 3 hour drive each way, my wife was like “we should clean the car first”… I was like it’s just gonna be covered in damn snacks as soon as we leave the driveway, why bother.

Make sure you get the Slimfit3LX. The "regular" Slimfit is actually too wide for 3 across.   In order to get 3 across in almost every vehicle, you'll need to use the seatbelt install for all 3 seats. That allows you to pull the side seats closer to the door to maximize space. (You also must seatbelt install when the child hits the maximum weight for lower anchors as well-- often but not always 40lbs-- so it's wise to get familiar with doing that as eventually you will need to do it all the time.)   With rental cars, you'll want to look for the biggest vehicle you can to maximize the likelihood of the seats fitting. So a large sedan instead of an economy or compact, for example.   3-across installs I've personally had good luck with:   - Chicco Keyfit, 2 RF Slimfit3LX   - 2 RF Slimfit3LX, FF Chicco MyFit   - RF  Slimfit3LX, FF Diono Radian, RF Slimfit3LX  Keep in mind that the Slimfit tends to tilt slightly when installed rear facing with the seatbelt. This doesn't affect the safety as long as it is tightly installed (moves less than an inch at the belt path when you give it a handshake with your non dominant hand). But don't be surprised when it happens! It's just an annoying bug with that particular seat. Forward facing it's doesn't have that issue.

Convertible car seats(5lbs-100lbs) tend to be large and bulky and suck to use for years. I personally prefer the Diono brand car seats. They are low profile, easy to fit 3 across a bench seat, FAA approved, foldable for travel/storage, good for 10 years, easy to adjust straps, and they have a metal frame in the for durability. They are pretty heavy and a bit of an investment but in my opinion 100% worth it.