Nobody is mentioning about adding a membrane so you won't get cracks. The contractor that built my house didn't use that and my tile is cracking from the foundation slab cracking. I was told if they installed a membrane it wouldn't have cracked. :mad:
Just bite the bullet, and do it the right way. Take the old tile out. Then put a membrane down and tile over that. You won't get crack if you have a concrete slab. :D