While milk thistle is good for the liver, it is by far not the most potent liver protector, and basically any supplement with several ingredients will surpass it. That is quite interesting that you got allergy to milk thistle - that is extremely rare. Are you sure it was not to one of the additives in the supplement?
As for the liver protection, you can take festal, essenciale forte, NAC, TUDCA....ideally you would be taking N2Guard, as it has over 30 ingredients. However, it does contain milk thistle, so I don't know how your body would react to it.