Well, that's an easy one to find. I listened to the whole thing through Audible last year. It's narrated by Amy Landon, who does a really solid job—her voice for Beth is so detached and precise in the early parts, which fits perfectly. The production quality is clean, no weird background noise or anything.
If you don't have an Audible subscription, check if your local library uses Libby or Hoopla. Mine did, and I got it with zero wait, which was a nice surprise. I'd avoid random YouTube uploads; they're usually chopped up and the audio is terrible. Just get it legit, it's worth it for a story that leans so much on internal monologue.