It depends on what you're most concerned about? Price, convenient location, or how often you want to train. There are many gyms in Pattaya. I know of Battle Conquer Gym and EVO360.
Actually, if you're comfortable handling it yourself, that's perfectly fine. all the comments here are already helpful. But if you'd prefer the peace of mind of guaranteed approval, I can assist you and offer a full refund if your visa is rejected. We have done in Australia before.