How can I keep myself upright while sleeping?

Seems like this would be a simple thing to do, but even with a wedge pillow I seem to slide down. Reflux wakes me up. I stop eating 4 hours before bedtime, but continue to drink water. I had an Ivor Lewis esophagectomy 4 years ago. For the past few months, I have had an irritated feeling in my throat & a dry cough. More recently, I have had occasional problems swallowing liquids - seems to go down the wrong way & sets off violent coughing. I’m worried about aspirating, but that’s another issue.
Any ideas for better upright sleeping?