Four Month Old Choking

I'm posting this here in case some of you who have babies with reflux might be able to help, as I'm thinking that some of the same things might work. We are looking for ways to help our little man at night. He is four months old and has global hypertonia (which means his muscles are really stiff), this causes him lots of issues but one of the ones that worries me the most is that he chokes frequently on his saliva especially at night when he is flat in his moses basket. He's still in our room, but I hate leaving him for even short amounts of time, as I know it could happen. Apart from anything else it's really distressing for him, especially now he is more aware of what's going on. I'm thinking of getting a wedge for the moses basket to help and I'm also considering getting a different type of baby monitor which will keep me better informed about him so I worry less when I nip downstairs and we're off to a specialist centre in London for a week in a few weeks. I'd love any other ideas people have, as we are more than up for ideas of how to help him.