Wedge for bassinet?

Jordan

9 day old son has reflux and starting to spit up in his sleep.

Nurse said to put a wedge in bassinet or sleep in car seat. I'm not gonna put him in a car seat to sleep, I only feel comfortable with him on a flat surface, swaddled.

Our bassinet is the arms reach versatile.

Is he okay to sleep on back even though he has spit up.