I have a thoroughbred with thin soles. I have had him only since February. The first thing I did was add copper, zinc, methionine, biotin, and lysine to his supplements, as all are important to building healthy hooves. Then I searched for the right hoof trimmer, which in my case meant finding a barefoot trimmer. After trying a local barefoot trimmer and a farrier I have finally settled on a barefoot trimmer who, IMO, knows what she is doing. I have to pay an extra trip charge for her on top of the trim charge because of the distance, but I just do what I have to do. You might have to search for an experienced barefoot trimmer who knows what they are doing. Ask for their training and education credentials, and for references.
I have also put a hoof dressing on to try to keep moisture in, but haven't used it consistently. There are different thoughts on the usefulness of hoof dressings but I thought it couldn't hurt - might help. Hoof dressings by themselves will do nothing if you do not have the diet, supplements, and trim in place.
After the trim, I would recommend putting hoof boots on your horse for turnout. I did not do that and my horse ended up with an abscess.
If you are riding him/her now, use hoof boots.
Barbara Rosensteel (and Ranger)