If your going to rock out a Charizard than you should worry about Stealth Rocks. SR is the main reason Charizard is not OU(In my opinion) It takes serious damage that does not go well with a Belly drum set.
So I would suggest a spinner in your team like Donphan or Hitmontop. Donphan might be a good choice for the switch in (Besides an attack from water of course) and be able to take out the rocks easily.
Donphan@Leftovers
252 HP / 252 Atk / 4 Spe
Adamant
Sturdy
-Rapid Spin
-Earthquake
-Stone Edge
Ice shard/Roar
This set can help out Your Charizard vary well with getting rid of rocks and most likey causing whatever was taking on your Charizard to switch out.
Another option is Gastrodon for the amazing switch in and it can handle just about anything they would want to take down your Charizard with.
And Jolteon is a good choice, vary strong,fast and if you can pull off a Sub into Charizard than I feel bad for your opponent
And I another suggestion could be in stead of Fire Blast maybe going Fire Punch. With the Blaze and a Belly Drum raise Fire Punch could give them hell, and you dont need to take the chance with accuracy. If you missed with a fire Blast than that could back fire your whole set up. Just a suggestion.