Reflux is a common problem with babies, a reason is that you put your baby in bed too early after feeding it, but some babies also were born with this problem.
My boy was born with this problem. 3 years after, it has to be controlled by taking care of the food he eats depending on the time of the day.
An anti-reflux pillow is a great tool to help your baby with this problem.
There are different models of pillows. Some are made to be put under the Mattress and others are very soft so you can put your baby on them.
The ones you can put your baby on, should be soft and the material should prevent your baby slide down.
On Amazon you can find very good pillows that may fit your needs.