Shinseiki / 20th Century Type can set some fruit alone, but it does better with a partner. Pears often crop more reliably and carry heavier harvests when another pear blooms nearby. It flowers in bloom group 2, which is early bloom, so a partner has to be flowering at the same time to be any use. Usually grown in USDA zones 5-9.
No single variety stands out as the obvious partner, but that is not a problem here: Golden Spice, Juicy Jewel, Parker, Summercrisp, and Twentieth Century / Nijisseiki all bloom close enough to work. There are 4 more in the list below. Pick whichever your nursery actually carries. Try to keep partner trees within about 50 feet when possible. Pear bloom can be damaged by late frost, so a partner adds insurance.
One thing to keep in mind. Penn State notes that Shinseiki can set fruit by itself, but still benefits from cross-pollination.
To put that into practice: at a minimum, plant two pear varieties with overlapping bloom whenever you can, even if one is partly self-fruitful. Better still, plant two to three pears with similar bloom timing so cool spring weather or weak bee activity does not leave a tree without pollen. If space is tight, keep one productive pear and add one dependable pollinizing partner rather than relying on a single tree to crop heavily every year.