Hi, I feel your pain, literally.
I had a L4-L5 Anterior (front horizontal incision under my belly button) and a Posterior (vertical incision on my lower back) Lumbar Fusion with Allograft performed in 2025.
The Titanium cage that was placed to secure the vertebrae shifts slightly when I lie down in bed at night. I struggle to get my back to relax but have learned that placing an object that looks like a metal bookend against and under my spine...actually allows my back to relax after about 10 minutes max and then I remove it and can get on to sleep. I also use a small hand towel folded behind my back when I'm in our vehicles which helps too. It's like my back just can't relax anymore and I can feel the cage because I'm very thin skinned on my back. Hope some of this helps you.
Wishing you better days ahead.