I also would recommend renting one of the jogging strollers from Magic strollers or Orlando strollers. If you don't use it at home, no use in purchasing one. Sure it probably costs the same as buying a volo, but in my opinion, your ds is too big for the Maclaren volo. I think he'll look pretty scrunched in that one as well. My almost 5 yr old dd is 38 lbs, and 42 inches and looks too big for it. We also have a BOB duo, which is similar to the jogging strollers the 2 companies above rent, and she has lots of room in that one.
My dd will probably walk most of the time when we go, but we plan on renting the double from Magic strollers for our 2.5 yr old, adn then she will have a seat if she wants one. We would love to take our BOB, but I know both my dh and I will be uncomfortable leaving it (it's too pricey to risk). Both Magic and Orlando rentals have the option to add insurance for $25 that covers you during your stay. Worth it for our peace of mind!!