Small Props for High Altitude

I am new to boating and need help selecting a prop for my 2017 Margay with a 150 hp mercury 2 stroke. I will be running the boat at around 4000-6000 feet elevation. Everyone has told me I will need a smaller pitch prop than what is on the boat now. Currently it has a 21 pitch Solas lexor that was used on lakes around 1500 foot elevation. Any recommendations on props for this hull that come in smaller pitches?