We had a firm, home-style mattress custom-made by an Amish craftsman in Ohio's Amish community near Mt. Hope, Ohio. We took the measurements to another Amish lady living just a mile or so from the mattress shop. She made a fitted sheet that works just fine. Always good to support the local business community.
For those wondering how?, both shops had diesel generators to operate the professional machinery in their respective shops. Some Amish sects do permit and encourage such "modern" adaptations for their productive business enterprises, so long as they are "off-grid" from our "English" power supply.