It is more common to say 'I decided to HAVE A shower' otherwise there is a question hanging of 'what are you showering? ... plants with water, your children with love, your partner with kisses...'
Without further reference, there will be no confusion about it. Some people say "take a shower"; others "have a shower"; still others just say "shower". For English speakers, the expression is clear. The action of the French reflexive verb is on the subject.