For a baby with reflux a crib wedge can be very helpful for sleeping. A wedge like this one from DexBaby can safely lift the crib on a slight incline.
And parents of babies with reflux love the Fisher Price Rock n’ Play for naps and lounging because it has a slight increase. There are two versions, I recommend the auto rocker one that moves without your assistance.
If your baby is old enough to hold his or her own head up, you can use a supportive seat such as a Bumbo after feedings to keep him upright. Note, babies should not spend a long time sitting in seats that prop them up but they are great for short periods of time.