BumbleBum

How old is your kiddo? We have just about every version of travel car seats bc we do long haul travel a lot.  For the 0-3 crowd, the Cosco Scenera is perfect. Cheap, light, straps easily to a travel stroller using a luggage strap, so you just strap it on and strap your kiddo in, for getting around the airport. Also cheap enough to be left behind if you only need it in one direction.  For the 2-5 crowd, the WayB Pico (FF only) is really nice. Also light, though you’ll want the backpack that’s another $80+ to store it if you’re going through airports. Kind of a B to install, but really compact and nice.  For the 4+ crowd (we started at 3.5,which is a bit young tbh), the Ride Safer Travel Vest is amazing. They wear it and you clip the seatbelt into it. It also has an optional top tether just like a FF seat’s top tether, for an added layer of security.  For the 6+ crowd, the bubble bum inflatable bum booster is great. 

We have a Cosco Finale. It's super light (like, easily heft it with one hand; we sling them over a shoulder if need be, but typically check them for free with the airline when we fly so as not to bother) and affordable, with a 5 point harness up to 65 lbs and then can convert to a backless booster (up to 100 lbs). Might not work for a plane, but we feel comfortable with our kid using the regular lap belt now (thought I've looked into the CARES harnesses). We do also have a Bubble Bum seat, but we prefer the Finale.

I am a CPST here in the US, so I have an extensive collection of car seats. I do a baseless install with a Nuna pipa, but I just installed the revolve slim today for my 1 year old (he is small) my 4 year old uses a Graco tranzitions and my 6 year old uses a bubble bum inflatable booster. My 4 year old has also used a ride safer travel vest. I’ve seen people manage 3 across with the graco slimfit. I’m not sure what seats you have access to. It’s doable though. My kids haven’t complained about being cramped when we do 3 across. We don’t drive more than 2 hours usually in one direction. If we are doing a longer trip, we drive my large suv.

We used an inflatable booster (Bubble bum) starting around that age. Biggest issue is keeping the kid ON the booster, lol. It’s smaller and they can slide off if they move around a lot. I also found that ours in particular didn’t last super long - maybe a year or two but I did have to do a repeat purchase in the not super large window that we needed it. The cost and convenience are good though.

We use the Bubblebum blow up booster for travel. I absolutely love it. It’s very easy to deflate and packs up about the size of a small umbrella. I will say though, we carry it for ubers in the city. I don’t think I’d trust the safety for freeways/long drives.

I bring a bubble bum inflatable car seat for Ubers. It deflates/rolls up to around the size of a water bottle. Taxis we usually just go without but we’ve always only used them for pretty packed surface streets

Also like the ride safer vest. FWIW, bubble bum did not work well for us and, imo, did not position my kids or the belt as safely. (It was okay for my 9 year old, but not great for my 7 year old. Both my kids are small for their age.)

I would just buy her a Bubble Bum booster seat. It inflates and is easily packable for travel.