I know people who have had GREAT success starting with a rope halter and then converting to a bit. Conversely, I also know people who have found it works better for them to start with a bit.
I personally think that if your horse is well-trained to the halter, you would find it easier to start it in a halter than with a bit. If you teach the horse that the rein doing this means that, you may never need to touch its mouth. My aid on the halter for my (7 month old) baby is soft constant pressure, then soft rhythmic pressure (check-release, check-release) slowly stepping up until she responds. 99% of the time she responds to phase one or two. That's for halt/back up. I don't need to touch the halter for her to turn or come forward, but the same principles would apply (in MY case, for MY horse) if I did. Generally speaking, if your horse is soft on the rope, it will be softer on the bridle when you break it to saddle.
Something that might help you is to improve your groundwork too, if there are any gaps. Does your horse move his hindquarter and shoulder independently when you ask? I'm working on it with my girl and she's 7 months old. At the moment I'm just satisfied with either, or both, going sideways, because I'm teaching her the concept of going sideways when I ask. I find that if they understand sideways on the ground, it's easier to teach it under saddle, and ALL horses should know how to move sideways off the leg, no matter their purpose.