Yes double bridles are wonderful. I started using the double around 45 years ago, and I have used them off and on, and I am a Forward Seat/hunt seat rider.
The last horse I used a double bridle on–well it was an amazing transformation. He was puzzled, puzzled, puzzled by the bit even though he is in his mid-late 20s. He is superbly conformed–to resist each and every rein aid (thick low set neck, downhill QH). He finds it so easy to set his lower jaw and just bull on through to wherever he wants to go. I had made great strides with various snaffles (best in the Wellep double jointed snaffle) but I always got this feeling of confusion from him, even when he learned decent contact and I taught him that the rein aids actually meant something. Inverting, gaping, and setting his lower jaw were his favorite defenses.
I measured his mouth, bought the correct sized bits, and with my riding teacher’s permission (her “lesson” horse) I made up a double bridle. At first I had a stainless steel ported Weymouth (with curb chain and lip strap) and a stainless steel French link bridoon. I thought he would simply freak out (like he normally does) but he accepted the two bits in his mouth calmly and for the first time riding him he stopped setting his lower jaw to make is mouth iron hard. After the first few rides I realized that he was comparing the two bits in his mouth when I gave a rein aid and he finally started to UNDERSTAND what the bit actions meant. He became much more cheerful in the riding ring for me.
Then I switched to titanium double bridle bits (Fager Mullen mouth Weymouth, Fager single-jointed titanium bridoon) and he improved even more. His lower jaw relaxed, his tongue relaxed, and he gaped a lot less because he was starting to understand the whole thing about a bit in his mouth. It was with the double bridle that I realized that under all the defensiveness, anger, confusion and fear was a really neat little riding horse!
The only reason I am not riding him in the double bridle now is that I FINALLY found a snaffle bit that he LIKES (as noted by two riding teachers at the stable,) the Fager Bianca double jointed snaffle with a roller in the middle. This is the only snaffle with which he is as responsive as in the double bridle, as relaxed as in the double bridle, and happier than he was with the double. I wanted to go back to the double bridle with him but he is so happy with his new snaffle I really hesitate.
Thinking back among the five horses I’ve started in the double bridle, three of the horses used the double bridle to FINALLY figure out what the bit actions meant. Once they figured this out it was easy to go back to the snaffle and get a decent ride.
With my MS I find having two reins in my hands sort of challenging, but the results are really, really worth it!
Have fun with your horse as both of you learn how to use the subtlety of the double bridle to get superior results with a lot less force and a lot less confusion on the part of the horse.
There is a reason why experienced horsemen in the hunt seat/dressage/saddle seat riding schools often prefer to ride most horses in the double bridle. Yes, one can get equivalent results in a snaffle, but to get these equivalent results a lot of riders have to use a dropped-noseband/flash strap/figure-eight noseband to even start getting the same results that they could get with a double bridle with a lot less work and a much happier, more comfortable horse.