Baby sleeping flat

FTM here so I overthink everything and get super anxious. We have a cradle for our son to sleep in next to our bed. I 100% understand the importance of him sleeping on his back and he will be doing that, but does anyone else find it uncomforting for their baby to sleep flat on their back? I'm just worried that if he is he flat and spits up or something, that he will choke. I've thought about finding some way to prop his head up a little higher than the rest of his body, but can't really think of how to do that because of how our cradle is shaped and what not. Any experienced moms out there have comforting words for me so I don't just sit there staring at him breathe all night? Lol