First of all, instead of contacting a forensic pathologist, contact a medical malpractice attorney first. There are attorneys that specialize in medical malpractice litigation against hospitals or care facilities and many of them have in-house nurses, physicians or other specialists who can go through the medical records to see if anything looks amiss. Before meeting with the attorney ask if you should bring a full copy of the patient's chart(s) with you for their review. Sometimes there are several facilities involved: a hospital, nursing facility and hospice. Most attorneys will want a complete set of all the records to get a sense of the complexity of the case. Make sure you write down all your recollections of what the doctors and nurses said or did that concerned you and the dates (if you remember them). When you meet with the attorney, these notes will help you remember what happened, and they may be disclosed to opposing counsel if you ever get deposed, so keep them clear of extraneous notes or unrelated private information.
An attorney can guide you in deciding whether you need an autopsy. The attorney will also know local practitioners that are reliable and good at both performing an autopsy and testifying. Performing an autopsy is considered the practice of medicine in most states so it is best if the attorney gets someone who is licensed in your state. The more local the pathologist is, the less the cost will be to you, because of travel fees. If you do not want to sue, but just want to know exactly what the cause of death was, consider having the autopsy done at a hospital where the patient recieved medical care. Many teaching hospitals will do these autopsies for a reduced cost or for free on inpatients because the autopsies are used to teach pathology residents in training. But if you are concerned about trauma or malpractice, it is best you get a forensic pathologist who is board-certified in forensic pathology by the American Board of Pathology. Most importantly, if the death is in any way due to trauma (a subdural, fall from bed, a hip fracture) or there are documented allegations of abuse or neglect, it is required to refer the case to the local Coroner or Medical Examiner and have them perform the autopsy. If you get resistance from the local Coroner because the hospital reported the death as "natural" then you should notify them of the trauma, and you may need to file a police report or call adult protective services to file a complaint about the abuse or neglect in order to encourage the Coroner to do an autopsy. This is important because only the Coroner or Medical Examiner's autopsy has the legal standing to prompt a potential criminal investigation. Also, most hospital autopsies don't collect toxicology so they won't be able to address questions about over-medication. That said, your perception of "over-medication" in a dying hospice patient, may actually be appropriate end-of-life care, so please consult a professional in order to interpret prescriptions, toxicology reports or pharmacy records.
Be aware that sometimes an autopsy can't answer all your questions. An autopsy is very good at showing what was happening at the time someone died, and figuring out what caused the death. If a wound has healed or a disease has been treated prior to death, the pathologic findings may have resolved and not be immediately visible at autopsy, but the consequences to the patient should be evident in the medical chart. Therefore, make sure the pathologist who does the autopsy has access to the records ideally prior to the performance of the autopsy, or at the very least prior to completion of the autopsy report.
Finally, before you embark on the arduous task of delving into the death of a loved one, be aware that malpractice litigation can take many years and the process of litigation itself can be a stressor on the family that can prolong the grieving process, delaying closure. If there are other members of your family that disagree with your assessment and want you to "let it go" you may want to talk to them and see if litigation is really the best path forward for everyone involved. Make sure you have plenty of emotional support throughout the process either from friends, relatives or spiritual/religious counselors. It will help you heal.