Brand new to this forum but have been reading for a while. I had a sort of similar issue that I thought I would share...
I'm an experienced rider and owned/rode for 20 years, but had to give it up when my son was born with major medical issues. Long story short, after 10 years of doctors, hospitals, weekly physical/occupational therapy and focusing everything on him, he is doing very well and I can add a horse(s) to the farm again.
However, I had to consider my son in my horse decisions. While he's doing great, he has no confidence with large animals, only small ones. Plus, he is about the size of a twig and he lacks the deep core strength he would need to sit a trotting horse, ride a bike on his own, ect.. (he's still in physical therapy for development of that.)
I've previously ridden many types, breeds, and diciplines of horses, including several gaited breeds and decided a gaited horse(s) would be a good horse for us. Finding a horse of any breed than can give an experienced rider a satisfying ride then turn around and embrace his inner therapy horse for a child is a tall order! Yes, most gaited breeds have big engines and like to go and darn near every gaited horse (no matter which breed) I saw seemed like that. It made finding the right gaited horse very frustrating and while I found plenty that were suitable for me, they would have really intimidated my son. I nearly decided to buy a "me" horse for me, and a special therapy horse just for him. However, I was convinced there was one out there and I was going to search until I found him/her!
I had to really widen my search area and take my time, but take heart... I did find the right one and I think you will too. It so happens my guy ended up being a Kentucky Mountain horse who has a slow and mellow engine. He's not a steppy horse, but gaites very well and extremely smooth. He was also regularly ridden by two little girls who are 7 and 10 years old. Good thing to have on his resume for sure!
My main focus/search was TWH, gaited Morgans, Appys (that do the Indian Shuffle) Missouri Fox Trotters, Rocky Mountains, Spotted Saddle Horses, Kentucky Mountains and mixtures of the above. Having previously owned a Morgan I was partial to the idea of a gited one, but it was this particular KMH that won our hearts.
I didn't really find one particular breed to be better for the bombproof horse as a whole, but for an adult who wouldn't need a "therapy horse" minded horse, I did find several really nice "suitable for new timid adult rider" type gaited horses with slower engines. They are out there.... take your time, see lots of horses, and you guys will find the right one.
Besides, searching is half the fun..... right?