You can run whatever you're capable of running right now as Ret and just change your loot specialization to Holy. The biggest thing you need as Holy is a weapon. After that you could probably start healing and slowly get rings/neck/cloak/trinkets. Everything else can stay the same. Strength changes to Int when you're specced holy for most of your gear.
the main items you need is 1 weapon, 1 neck, 1 cloak, 2 ring, 2 trinket
1 weapon - the easiest is to farm apexis to get the weapon and empowered it to 695
1 ring - buy the legendary ring quest
1 ring - either craft or buy from AH, or buy using apexis, or wait for baleful to drop while doing tannan jungle
1 cloak - either craft or buy from AH, or buy using apexis, or wait for baleful to drop while doing tannan jungle
2 trinkets - Encroaching Void, you can easily get 2 of these from tannan jungle, elite Putre'thar. this mob spawn in the same place when doing Assault on the Throne of Kil'jaeden - Quest
Don't forget there may be a few items around Tanaan jungle that you can loot that will fill in the off-pieces. I suggest downloading handy notes to see a visual representation on the map of where all the Tanaan treasures are. There should be at least a few int pieces for trinks/ring/neck/cloak etc.. I'm fairly sure there is at least one shield.