I agree with everything justdressage said - but here's some tips about bits.
With curbs, the shorter the shank is - in comparison to the purchase - the milder the bit. The purchase is where the headstall attaches.
Reins should always be loose with a curb bit, for multiple reasons. They have a long amount of warning of contact before any contact is had with a shanked bit. Also because if your reins are tight and you neck rein you'll be pulling the wrong side of the bit.
As for the mouth piece there are a number of styles. low ports apply a tiny amount of tongue relief, medium ports provide a great deal of tongue relief, high ports are full tongue relief but they put pressure on the pallet (roof of the mouth). There's also mullen mouth, where the whole bar of the bit curves otu away from the tongue without causing any pallet pressure. I like medium ports and mullen mouths.
Shank curves, the curve of the shank is also quite helpful, the deeper the curve in the more warning the horse has before the contact, it's also nice for grazing.
Broken mouth peices I wouldn't recommend for a curb bit- it's just too much.
But for broken mouth pieces, single jointed ones are the most severe - but also have the clearest communication for direct reining. 2 or more joints are milder (in most cases there are some obvious painful exceptions) they also provide clear communication for direct reining.
My personal choice for curb bits is a sweetwater bit with short shanks and a high purchase. Made out of sweet iron.
If you're looking for bitless options I personally find Indian Hackamores to be the best direct reining choice. They provide clear, strong communication - without pain. If you get the variety with metal rings for the reins to go through the release is immediate and obvious, which so many bitless options lack.
Personally I don't like mechanical hackamores or english hackamores, they can just do too much damage in the wrong hands.
Good luck with your pony :)