How to do Hajj on behalf of another

Description

If a person intends to do Hajj on behalf of someone who is unable to do it because of sickness, or who has passed away, how should he do the rituals? Should he choose Hajj Tamattu’ [where one does ihraam for ‘umrah then after ‘umrah comes out of ihraam and does a new ihraam for Hajj] or al-Ifraad [where one does Hajj only]?