with 5 boomkin you can probably kill mobs easily enough to have cloth gear. cloth is awesome. dont be afraid to use it if it improves your stats.
i tell this to other classes as well, hunters dont need to have mail gear completely, as well as pallies dont need to have everything plate. whats important is the gear, especially when fighting ranged. i was running a holy pally through an instance and some really nice mail pants dropped. she wouldnt take it because it was mail, but i told her she's giving up 200 armor points for 15 int, 12 stam and 10 strength, plus three sockets. wtf?? i'd give up 200 armor points in a heartbeat for that. so dont be too bent on just getting leather and thats it.

if you're a dps-cat, then yes, leather is what you want. but for boomkins, if you dont want less damage, use barkskin. or use entangling roots while you nuke.
i would do one entangle roots, the four moonfire, then wrath. mob proceeds to die. easy enough? lol