Looking for advice re: harness or booster

I have two DD's.

One is 3 and one will be 8 in April.

My 3 year old is in her sisters old True Fit in my car and Marathon in DH truck.

7 year old (48 inches and 53#) is in a Radian in my car and Frontier 90 in DH truck.

Both the Marathon and True Fit are expiring and I need to make a decision on what to do with seat arrangements.

Ideally I want to keep my almost 8 year old DD harnessed. We both feel it is much safer. However, the thought of the expense for 2 new seats is also killing me. So I am here for advice.

I drive a sedan and very frequently have a 3rd kid in the car. True Fit on driver side, Radian on passenger, booster jammed in the middle. (Also looking into options on that: Bubblebum maybe? MiFold?)

Anyways, what would you all do? Buy the 3 year old DD 2 new seats? And if so which seats do u recommend?

I should also mention, I am against majority here and am not a fan of the Radian, minus the small footprint in my sedan. It is too heavy and a PAIN to install in my sedan. I can install both Britax in my husband truck in 30 seconds perfectly, and would like something with ease of use for sure.

Thanks SO much!!!

I'm really happy with the Harmony Defender. It harnesses quite long and is high quality for a $100 seat, small footprint is a plus as well.

However, I'd probably get a booster for your almost 8 year old. A properly fitted booster compares to safety of a harnessed seat =)

I would look into a dedicated booster for your 8 year old. We don't have any data to suggest that harnessing is safer for a child her age, and it would be less expensive to invest in boosters at this point.

The britax parkway might work for her as it is relatively narrow at the base and has the slideguard for an extra point of restraint. We really liked ours and were able to fit it into a few three across scenarios.

Other boosters you might like: chicco kidfit, recaro performance booster, diono monterey, graco turbobooster/turboboosterlx/affix.