I found this ikea high chair cushion really handy when my baby was small as it helped to support him sitting up to eat his meals

Love this chair cushion! It’s so cute and comfortable and easy to use! Installs in seconds! Also very easy to clean! Just throw in washer

It is very easy to use. You just fill it up with Air and put the cushion on, then it is ready to use. So you just fill the Air up to the size you want to use.