I had/ have this problem too. I went to a specialist who made a 3d scan of my thumb/hand and gave me a special brace specific for my hand and needs. It is quite expensive though.
Before this I just went to a shop with braces and bought one like this
My specialist told me that the silver ones aren't that helpful if your thumb dislocates often because it can still dislocate while wearin one of those. The most important thing is having a brace that helps stabalise the whole bottom part of your thumb. So only the tip joint should be free. I.e. something like this won't do much to help against dislocating.