The Kobo Go HD is discontinued. Your best choice would be the Kobo Aura H2O Edition 2.
With the nook, I think you have to go into the font menu and select something like publisher font to show the embedded fonts.
But in looking for a font that is dark enough for eInk, you should give my modified version of Charis SIL (called ChareInk) a try. I use it and I don't need to up the weight at all.
https://www.mobileread.com/forums/sh...d.php?t=184056