Procollar (or neck hug) is used to stop the dog from lying flat which allows fluids and food to accumulate in the esophagus and helps to prevent aspiration pneumonia. This popular collar is called the pro collar and  has an inflatable pillow which helps to keep the dog’s head elevated to reduce regurg and coughing at night (or daytime if worn at all times except when eating )when the dog is lying down.They can either be inflatable or soft material. Is fastest for now to  buy an inflatable one in a pet store. You can buy pro collars at most major pet supply stores or online (see below links). Many of the ME owners prefer the stuffed pro collars over the inflatable ones ( as some dogs pop the inflatable ones).

Here are a few links for purchasing on-line :

Can also use the human neck hugs and sew Velcro to each end to close
Boppy pillow
Memory foam molded neck pillow and sew Velcro on ends to close

From someone who has fostered and owned dozens of ME dogs/puppies:
“You can buy them at PetCo or Petsmart or online. The Kong ones are the best for the money and come in various sizes.  I would use it at all times except when she is eating.”