I have a new to me paint gelding, around 10 years old. I don't know the history on him or which bit he used. He neck reins and seems very light on the reins. After reading a lot about bits, I am interested in a trying a swivel shank with solid mouthpiece. I want to continue neck reining him and am planning on routine, easy going Western trail rides on my property. A trainer came over and we used a snaffle on him. He did not like it at first but eventually settled in. My experience level is novice.
I'd ask your trainer for their opinion. Your trainer should also have some bits for you to try before you buy. Your horse may have also just not liked the mouthpiece of the snaffle you tried. That being said, you may need to stay in a snaffle for a while, your horse may be ready for a curb but you may not be. Novice riders, for the most part need some time to develop soft hands and doing so in a snaffle is much kinder to the horse.
If you ride without contact, and with slack in the reins, then a curb bit can be gentle enough. Just don't snatch on the reins with it...a smooth gentle consistent pull if you need to do so will give the horse warning before any real pressure starts.
I also had good results using this similar to this:
But it is very hard to give advice since horses & riders are all different. My mare really took to curb bits, while other horses won't use them. My Appy gelding doesn't care what type of bit you put in his mouth as long as you don't use it...which is not bad advice from a western perspective. He'll do just as well in a single joint snaffle as a curb or vice-versa.