What a lovely quilt. I also have some & plan quilt in future.
My suggestion for getting linens white. I put warm water in bucket --add drops of laundry soap and mix in a scoop of OXI clean. Soak the cloth for a day or two then rinse well. If you are in a sunny area lay old sheet on grass then lay linen/case/ cloth whatever on the sheet out in sun for it to dry. May have to repeat. For yellow type from head sweat I also use "GOOP" which is a hand cleaner for mechanics bought at hardware etc store. It's a white cream that I used for years to take marks off clothing.
Rub the goop into the damp pillowcase --put aside for few days then wash/dry. Will not harm colors either
What fabric and color did you use for the back of your quilt? Think that's all my questions.