I'm sorry you are having these problems.
You have good questions lined up for your doctor. Write them down so you don't forget to ask about each concern.
Your GYN will be able to go over your treatment options and risks with each treatment and how to monitor your lining to ensure your safety/ lessen your risks for progression toward cancer. Some women opt for hormonal therapy (with progestrone) to keep the lining thin, mirena might also be something to ask your doctor about.
A D&C should thin down your lining (how to maintain a healthy lining will be the question.) A D&C will also provide more cells for pathology exam than what the endometrial biopsy did, to be sure there is no atypia, etc.
I don't have any dietary suggestions (sorry) other than if you are overweight, losing the excess pounds is recommended because our fat cells are a repository for estrogen. Again, good questions for your doctor. I'm not sure if your polyps and hyperplasia also caused you heavy bleeding, but if so, your GYN should have suggestions for keeping your iron stores healthy too.
A second opinion is always a good idea when we are making major medical decisions. When cancer risks are a concern, it's a good idea to obtain the opinion of a GYN-Oncologist since that's their area of expertise.
Good luck at your appt. Hope all goes well and you come up with a game plan you are comfortable with.