Do you know of any mattress manufacturers/ makers in the Harrisburg, PA area?
Post #2 here has a list of the better options centered on Harrisburg, PA.
A little further afield to the west and east of you … Post #2 here has a list centered on State college and there is larger list centered on Philadelphia/Wilmington/Trenton areas in post #4 here and post #6 here has a list centered on Lehigh Valley, PA.
These cover everything I’m aware of within reasonable driving distance.
Hope this helps. I would start with a few phone calls to talk about some of your needs and preferences you already know about and to get a sense of which ones you most connect with before you visit. You have some good options available depending on what type of mattress you prefer and the distance that is convenient to travel.