Yolina, have you given my modified Charis SIL a go on your PW? It's been thickened up and the line space has been modified so it's not giving you overly large line spacing with KF8 eBooks. The link to it is earlier on in this thread.
Also, I have a larger version that sort of matches the size of the default Kindle font. But still gives better lin spacing and better letter spacing for more text on screen.