FF seat for car without adjustable headrest

Originally posted in r/parenting but also trying here. Please note that I would rather not remove the headrests unless that’s the only option since it seems to require tools and wouldn’t be super easy to reinstall (and would potentially damage them).

We are getting ready to forward face my almost 4 year old. She is 32 pounds and like 40 ish inches (idk exactly). We have two cars and she is currently in a nuna revv in both. The plan is for our infant (not even 3 months) to move into the revv seats and we’ll get a forward facing/ converts to booster eventually seat for toddler.

The problem: I drive a 2018 Volvo XC60 and the backseat headrests are not adjustable. Apparently that makes it really hard to get a proper install for a forward facing seat. Every review I read for every single seat just says be cautious and you have to test it out in your specific car. Basically, the seat cannot be pushed forward by your headrest but it’s impossible to say if that will happen unless you try it?

I took the online quiz on car seat for the littles and it said the only seat that will work for my car is the Nuna Lumn, which is $680. I do not want to spend that much since I have to buy two seats.

I also have no idea where I could try to install the car seat in my car without buying it first. We don’t have many places to check our car seats - it’s like Nordstrom and some speciality stores that probably won’t allow this. None of our toddler friends have any of the seats that we are looking at so I can’t ask them to try it out.

Has anyone else dealt with this? What did people do before the Nuna Lumn was on the market? What am I missing? This feels absolutely insane for a car that so many families must drive.