I believe you are looking for a guardian. This is a person that you select or is appointed to assist you by the court system.  A guardian is tasked with carrying out your legal, medical, and financial wishes.
In fact, a guardian may be a geriatric care manager, care manager, or a volunteer guardian. In most cases, the court will conduct an investigation to ensure that the person appointed as a guardian is suitable and will act in the best interests of the individual. Lastly, a court may also appoint a conservator, to manage financial affairs.