The two people you want are the counselor and the case manager. Those are your primary contacts for anything related to your son's situation inside the facility, whether it is housing questions, programming, release planning, or general welfare.
Call the facility's main number and ask to be connected to your son's counselor or case manager by name if you have it, or ask them to direct you to whoever handles his housing unit. If you do not know the unit, give them his full name and inmate ID number and they can look up who his assigned staff are.
If neither the counselor nor the case manager is available or responsive, the unit team secretary is another option who can often field questions or take a message. For welfare concerns specifically, the chaplain is also worth trying and tends to be more accessible than administrative staff.
Be patient, be polite, and follow up if you do not hear back. These calls can take persistence but they do get answered.