Mighty Crusader Expertise, just released, reads:
Benefit: When you are using a holy symbol and wielding a melee weapon in two hands, you gain a +1 feat bonus to weapon attack rolls you make with the weapon and a +1 feat bonus to implement attack rolls you make with the holy symbol. These bonuses increase to +2 at 11th level and +3 at 21st level.
Also, when you use two hands to wield a melee weapon with which you have proficiency, ranged and area attacks that you make with a holy symbol do not provoke attacks of opportunity.
I would like to take advantage of this as a sword&board paladin by using the versatile property of a longsword or equivalent. What feats, type of shield, or magic items do I need to have to be able to use a free action to switch between shield use and using my sword two-handed?