Okay, so I borrowed the basic idea from Monte Cook's book of hallowed might and the book of righteousnees, and then updated it to 3.5 and altered it a bit more. But is it balanced.
Basically, remove Turn Undead and Remove Disease from the paladin. The paladin chooses a clerical domain. At 4th level, she gains the domain power as a cleric of his paladin level-3. (If he chooses the Sun domain, she gains the ability to turn undead as a cleric-3 instead of the normal domain power.) Also, add the domain spells to the paladin's spell list, and add Remove Disease as a 3rd level spell.
I think if anything this is rather weak, but it is hard to tell. Removing the ability to cast a spell once per week and adding a spell to the lists are both very weak abilities. Trading turn undead for a domain ability could be strong, or it could be weak depending on the campaign and the domain. I'm just not sure.
Basically, remove Turn Undead and Remove Disease from the paladin. The paladin chooses a clerical domain. At 4th level, she gains the domain power as a cleric of his paladin level-3. (If he chooses the Sun domain, she gains the ability to turn undead as a cleric-3 instead of the normal domain power.) Also, add the domain spells to the paladin's spell list, and add Remove Disease as a 3rd level spell.
I think if anything this is rather weak, but it is hard to tell. Removing the ability to cast a spell once per week and adding a spell to the lists are both very weak abilities. Trading turn undead for a domain ability could be strong, or it could be weak depending on the campaign and the domain. I'm just not sure.