Our ENT told us not to bother with plugs in shower or bath. It's only an issue when ears are submerged in water like during swimming. DD is on to her 4th set of grommets and have never had an issue with bath or hair washing doing anything to the grommets or ear infections or anything.
I love the soggy froggy plugs for her. They mould properly like blue tac and stay in easily. Available online.