A driving bit is made different than a riding bit but mouthpiece choices are so many today you should have choices to choose your driving partner will enjoy carrying quietly.
These are a few images for Liverpool "driving" bits...different variations. So many to choose from, each different..
And one with showing the option of rein attachments that will greatly influence the strength of any mouthpiece you choose.
The same principle applies as with a riding bit...the further away you go from the actual mouthpiece the more oomph is transported to the animal in request made.
Also the headstall attachment adds more oomph as it is above the mouthpiece, not even with the mouthpiece..
Where you will find a difference is with many of the shank driving bits, is the ability to choose the rein position for added "leverage" if needed/desired or you can opt for connecting rein to the ring and remove the leverage effect.
I use to drive a team of Percheron in fun and competition settings...
We used bits of the Liverpool design of heavy shank hanging with a cross-bar for stability and so not to hook anything with that shank but the mouthpiece was more of a straight bar or slight arched mullen mouth...all our driving bits had curb chains we adjusted carefully and correctly to each horse.
I would be more concerned of a curb chain introduction be done slow so Pony understand the engagement of that bit for signals sent.
The bottom line is to me if Pony listened well to a simple single joint snaffle mouthpiece than that is what I would still keep in the mouth till needed to change.
If you had communication, listening and response to a direct rein bit of a full-cheek snaffle then the least amount of drop from the headstall and smallest shank possible may be all you need. Maybe a half-cheek driving bit is more than enough..