I play mostly as Oak as well (and a little QoT and Sedna)

Beginning - scale + banded + vlemish + nimoth  i avoid minion boosting since i typically dont get any minions until i can afford priests IV (then archers IV) and if i could use a wee bit more DPS then i'll get grunts IV for endgame

mid-game i go for hauberk + unbreakable boots and then platemail of the crusader. 

late game - godplate if i am lucky.

these arent minion boosting entirely since i have to worry about health & armor as well. 

The minions seem to stay alive pretty long with just hauberk and crusader.

Fell darkur gloves are also good for minions.

j

If you can handle having a weak DG but uber strong minions, here's a bunch of the minion related items. Check www.demigodDB.com for the stats.

Armor

Hauberk of Life - Nice HP boost.

Platemail of the Crusader - Very expensive but if you have the cash for it, it is also a good HP booster. I believe this is also the only item with minion regen.

Godplate - You probably won't need so my minion HP to warrent getting this.

Helm

Theurgist's Cap - Another HP boosting item along with some regen.

Gloves

Gloves of Fell-Durkur - Great for increasing minion damage and attack speed.

Gladiator Gloves - Smaller damage increase for minions.

Trinket

Forest Band - Adds armor to minions. Only effective if minions are taking tower or auto attack damage.

Twig of Life - Good item when fighting AoE DGs. Also adds small amount of HP.

Consumable

Sigil of Vitality - Most efficient minion HP item. Adds small amount of HP for extremely low price.

Artifact

Bulwark of Ages - Adds a moderate amount of HP and armor to minions.

Askandor -Adds plenty of extra attack speed and damage to minions.

All Father's Ring - Does everything and should be bought anytime you can afford it.

Ring of Divine Might DOES NOT WORK on Shamblers, I tested it. I can only guess that that's another embarassing bug which should have never existed. You do most damage with your Shamblers by Mulching them.