Convertible or combination seat

Hello all,
I am so confused. I have a 2.5 year old who is 28 pounds and 37 inches tall. she is in a FFing Britax Roundabout 55 in our family van (used once a week and for random long car trips) and a Britax Boulevard 70 G-30 in my car (used every day). My 5-month old son is almost 19 pounds and 27 inches long. He is getting too heavy for me to carry in the Chicco Keyfit.
Do I switch my daughter into a combination car seat and move my son into the convertibles rear facing or do I keep her in the Britax seats she has and purchase new convertibles (with higher weight limits) for him?
My concerns with a combination is that they seem so straight and she still sleeps in her car seat. And I am seeing most do not have a lock off for the belt (I think I need this). I want to harness for as long as possible and realize I may need to purchase combinations later anyways with the lower weight limits of my two convertible car seats (purchase two years ago). So do I go with combination for her now? And if so, which one is the best with lockoff? I have looked online at the Britax Frontier 90, Graco Nautalis, Recaro Performance Sport, and the Diono Radian.
Any and all advice (aside from turning her back around) is appreciated. I know rear facing is recommended as long as possible but it is no longer possible and she made it to two years old rear facing.

You could leave the Keyfit in the car like you would a convertible and reevaluate how often she sleeps when the baby grows out of it completely. A few months can make a huge difference in whether kids are comfortable being more upright to sleep.

safeinthecar said:

You could leave the Keyfit in the car like you would a convertible and reevaluate how often she sleeps when the baby grows out of it completely. A few months can make a huge difference in whether kids are comfortable being more upright to sleep.

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This very much. Lock-offs aren't required, as long as you can lock the belt. The Britax Frontier 90 is an expensive seat, but with the "click tight" feature, it is a BREEZE to install.

How much of the expiration date is left on your daughter's convertible?

I have 5 years left on both convertibles, which is plenty to get my son throw rear facing and probably some forward facing too. He will outgrow car seats faster than his sister because he is proving to be a larger build than she. I checked the van and I do need lock off on that car so I was thinking of going with the Frontier 90 for both, unless the install is easy enough with the click system that I could do the one Frontier and move easily between cars. I drop off and pick up from daycare the three days they go each week and in an emergency my husband could pick up my car from work as I work close to daycare (in the 2.5 years of her life, I think I have only missed two or three pickups so it isn't a big issue plus it could be my major excuse to always leave work on time)

Vehicles made after 1996 are required to have locking seatbelts but the method of locking varies. Before 96, you would still probably have lap only belts in center seats and you don't need a locking clip/lockoff for a lap only belt. If you tell us what vehicles you have, we will probably be able to tell you how that vehicle's belts lock.

My car is a 2004 xterra and the other car is a 12-passenger 1998 Ford club wagon (van). We will have the brt
I tax rear facing behind the driver seat in the van. Not sure where the placement will be in the xterra due to space wight the front seat.

Both vehicles have outboard seatbelts that lock when you pull the shoulder belt all the way out (slowly! pulling it fast can make it lock up right where it is just like in a crash) and a lap-only belt with a tail in the center position of each bench. No locking clip needed for wither vehicle.