It’s counterintuitive, but a well-designed font can have a lot of subtle variation between letters and still look consistent on the page. The converse of this principle is that a font with too much consistency can be numbing to read. Cambria is an example of this problem. It works well on screen, but on the printed page, it induces headaches. Guardian, Elena, and Charter are similar to Cambria but avoid monotony. (Charter is even available for free.) FF Tisa has a more relaxed, informal rhythm.
Source Serif Pro is another very good open-source option. It comes in six weights, but doesn’t have italics yet.