@beespeckled,
As Kolenka kindly said -- a serif-style font.
Any (or all
) of Amasis, Palatino nova, Really No2 would fit the bill.
To save you having to look for suitable text, page 3 (headed 'EPUB Serif Font') of this test epub would do nicely. It contains regular, bold, italic and bolditalic text all on one page. Or at least it does on a PRS650.