I plugged your team into an online team builder, and your team seems to be pretty well-balanced already.
You'll have to add a Ground resistance or immunity, though. Three of your Pokémon are weak to Ground, and only one is immune to it. A Ghost resistance or immunity would be nice as well, to patch up Metagross's weakness to it. As for other types to cover defensively, try not to add any more weaknesses to Rock, Electric, Dragon, Dark, and Fairy.
A Grass-type (like Sceptile or Ludicolo) or a Normal-type (like Exploud) would be your best bet. Lastly, try to look at Levitate users like Weezing. Apparently there are also Deerling in Route 117 after beating Kyogre, so you could add Sawsbuck to your team as well.