J pole is a nice antenna.. Built my first one like 45 years ago.
Still have a couple floating around though I'm changing the RV's antenna to a coxial Dipole Should be right close to identical performance.. You do know the J-Pole has another name as well don't you? (I will not say what it is I'm giving you a research project) Has to do with where they were first used.
Now as to your question.. A fiberglass flag pole would work well Strap it to the upper section...
Click Here For a company that sells a real nice telescoping pole.. Bit pricy but this puppy can take a small beam and rotor!!!