Best Car/Booster/Car Seat Combo for x5 OR Middle Seat Belt Extender Connector

*Reposting for clarification*

I am looking for actual car seat and booster seat combinations for our 2016 X5 for a car seat-booster-car seat configuration. Has anyone done this and liked what they ended up with? And if so, what are you actually using?

We’ve got a Nuna Pipa Lite and a Nuna Rava, with a Cosco booster (ordered Diono which may be inch slimmer). We can make this work but the seat belt for the booster is hard to get to.

Trying to find a seat belt extender for the middle seat but the middle seat belt is specifically made to not accommodate them (apparently). I did see someone completely swapped out the seat belt latch for an extended version although we would prefer not to go that route.

I cannot be the only X5 driver with a 0/2/4 year old so hopefully someone has figured this out!