I started a year ago transitioning to barefoot. One horse is doing great, the other is still tender. Definitely use boots when you ride or if your horse can wear them in a stall or paddock when he seems tender footed.
My Natural Hoof farrier said it could take two years to transition for some horses. Some never can transition. My understanding is Thoroughbreds do not have exceptionally strong hooves, so you may not be able to go Barefoot.
If you continue to try barefoot, supplement with Biotin to build a better hoof. It will take a year for the hoof to grow out to see if the Biotin is helping.
Recommended reading by my natural hoof care specialist: Making Natural Hoof Care Work for You.