I started off with 5 Shaman, but now I run 1 Paladin, 3 Shaman and 1 Druid, one of the Shaman is heal-specced. Even though the Druid is 6 levels behind, I still blast through instances, the resto Shaman really shines during emergency situations and Earth Shield means I rarely have to heal on trash (in my first Sethekk Halls run today, I only had to heal during the bosses and the final trash pull before the last boss).

But as you don't have a dedicated tank, my advice would be to stick with Elemental Shaman until you need a Resto, which may not be until you hit heroics or some bosses (I couldn't do the second boss in The Blood Furnace without a tank at level 62 :[ )

Also, it's resto, not restro, thought I'd save your R key some trouble.