I personally have not tried it but somewhere I read that some people use a Baucher bit in place of a bradoon. You might have to punch some holes in your bradoon hanger though.
I mostly ride the smaller horses–13.2 to 15.3, often with smaller mouths. It was a real adventure to fine double bridle bits small enough for a 4 1/2" mouth which were not stainless steel. Once the horses I ride learned that there is an alternative to stainless steel bits they have been VERY firm that stainless steel bits are no longer acceptable to them.
I ended up using mostly the Fager titanium double bridle bits, but they do not make a 5 3/4" bradoon. These people do make a 145mm titanium Weymouth curb, but they have unusual ideas about the proper relationship of the widths of the Weymouth and bradoon (which did work on three horses I ride). The Fager people say that they have found that if the Weymouth is around 5mm wider than the bradoon it does not interfere with the bradoon bit.
The only reason I’ve bought the wider double bridle bits is because there are so many WBs around now that take the wider bits. I no longer own horses because I am too crippled with MS to do the work, and anyway I do not get enough money in to board at a good stable (I have my own land if I just had the energy to take care of my own horses!) I’ve noticed more WBs in the riding schools and I like being prepared with suitable double bridle bits because double bridles rarely exist in hunt seat lesson stables any more and I have to provide my own.
I really like riding in the double bridle, and if I am expected to ride a super tall horse for me I would just rather do it in a double bridle since I am so weak.
WITH MY HANDS (and your hands may be different) the horses really hated the snaffles/bradoons that give “good” tongue relief, to the point of violently slinging their heads if I was rude enough to expect them to carry one in their mouths.