From what I have seen at the lower level TWH shows, and I am coming from background with Saddlebreds here, but have friends that are trainers of TWH, and Racking Horses, and on show circuit with them. The saddleseat suits are not used as much, from what I saw, they were wearing longish jackets and straight pants, in fact the men looked like they were wearing Sunday or business suits.
And the women were wearing egg yolk yellow suits, and fuschia ones, again with straight legs, and both pants and coats were colored. And the "hats" were little better than what you buy at State Fairs where they spray paint on a cheap see through straw cowboy hat.
A trainer, female, who showed Saddlebreds, but had a couple of customers who wanted to compete in the "speed racking" classes with their Saddlers, had her show in TWH/Racking shows, and she looked really great in her Saddlebred attire, but out of place, as no one else dressed like that.
And of course if your horse is going to be in Western classes, would follow Western attire there.
You can also subscribe to a TWH breed magazine, or check online sites and see what they people are wearing, so as to get a better idea of what is being worn.
But a saddleseat suit, is a good investment, and looks the best to me, and made to ride in, so it will fit right.
Can't wait to see what you decide on.
And can check out State Line Tack, and World Champion for their saddleseat suits.