Looking for advice: Liv Belive SL0 vs Liv Avail

I’m looking for a new endurance road bike (I’m a beginner), but unfortunately there’s very little stock available in my area. So I don’t really have the option to try different models side by side.
After a lot of Googling, I’ve narrowed it down to Liv, with my main requirements being: endurance geometry, Shimano 105 and hydraulic disc brakes.
With my previous bike (a Scott Contessa Speedster 15), I experienced quite a lot of lower back pain, so getting a good fit and a comfortable riding position is really important to me. I’ve also looked at the Trek Domane AL 5, but I can’t find one available in my size either.
I’ve now got two options:
Liv Beliv SL 0 – brand new
Liv Avail – used, but sold by a bike shop; full carbon and from 2025
They’re both the same price.

Which one would you recommend? I’m a little worried that the Beliv SL 0 might have a slightly too aggressive/sporty riding position for me, especially considering my previous lower back issues.
Any advice or experience with either bike would be greatly appreciated!
Thanks in advance!