Which would you pick?? Tippy probooster, "launching" Cybex, or backless??

I'm having a beast of a time finding something to fit in a wonky spot in our new-to-us vehicle. This is for our almost 8yo, ~50lb. son. I found three seats that fit, and all have major drawbacks.

- Option #1: Backless Literider. Fits like it was made for the spot. But there are no airbags back there, and he is not quite 8. Kinda gives me the creeps.

- Option #2: Cybex. This fits the spot pretty well. My almost 7yo tried it, thought it was uncomfortable, and his chest was thrust forward - he had to arch his back to get his head back into the headrest.

- Option #3: ProBooster. This fits the spot, and fits my son really nicely. Great lap belt position, and all around terrific fit. We took it on a test drive, and it does tip. Darn! Left turns are lovely. Right turns tip a few inches. Every time. Does that qualify as "unstable", and make it incompatable with the vehicle? Doesn't seem very stable to me - no other booster has tipped in that spot. BUT, seems like it would offer substantially more protection than a backless. His shoulder stays under the shoulder belt, just shifts position slightly as it tips.

I've done tons of searches, read everything I can find, and started several threads on this seat hunt, and these three seats are all I can come up with as my options. What would you pick if it were your child????

Is he new to booster riding? Sometimes new riders have a lot more motion than seasoned booster riders? If not, my PW used to tip like the tower of Pisa and my kids never complained about it, seatbelt always stayed positioned just fine, so I let it be. Recaro Start was perfect in the third row of my van, not tippy, tethered, but I wonder if you could find one anywhere?

Have you tried the Monterey? I have it and the pro booster and the Monterey is more stable even when not latched.

she tried the monterey there... it covers the buckle stalk...

I'd try the recaro a little longer and see what your ds feels about it.

I wouldn't use a booster that made him uncomfortable.

Have you tried a recaro vivo?

When the booster tips, it must be pulling more belt out of the retractor. I don't like it for that reason.

Is there any reason you can't put a pool noodle under the edge of the pro booster to keep it from tipping? I don't know why they wouldn't make the base the same width as the seat.

Are you allowed to recline your seat at all to make the cybex recline more?

If not, I'd probably go with the literider, provided the shoulder belt does fit properly without a back to route through.

The vehicle seat doesn't recline in that position.

Monterey is borderline fitting, but covers the belt anchor a smidge.

That spot is really a PITA.

Have you tried the cybex with THAT specific child. I know my daughter has never complained about the fit, could it be child specific? HTH