Epub Issues with NOOK readers

When compiling an epub, I’m having a hard time formatting it correctly for a Nook reader.

The epub is generated and when uploaded to a Nook, it reads just fine. Cover art, table of contents, text is all there. However, the font size or font cannot be changed within the reader. Line spacing cannot be changed either.

If readers are using the Nook PC app or the Nook reader itself, it is more of an annoyance to not be able to change to your preferred settings. And I want my readers to have that ability. However, if they are reading on a smartphone, it’s impossible to read without being able to change text size.

This is not the case when compiling for Kindle (mobi format). Changing text size and font is doable.

Can someone give me some pointers?

Thank you very much,