Link to next heading or section in Apple Pages?

I have a document which has 26 headings - for each letter of the alphabet.

At the start of, say, H, there is a heading which includes a link backwards to G, and another link forwards to I.

I export my Pages document to PDF and that works fine.

A viewer can jump to the next letter easily.

But if the section for H spreads over a number of pages, as it does, they have to scroll up or down to the previous or next heading to reach the links to G or I or J.

I'd actually like to have links to "next heading", or "next section" (I could add sections, if necessary), that I could put in the footer. Thus making it easy to jump backwards or forwards by a letter - wherever you are. I'd be OK with the word Prev and Next (or something like that) rather than the actual letters.

I've already got links to Table of Contents and End of document in the footer.

Of course, logically, I could have 26 letters in my footer and each would be a link. The trouble with that being space. I don't want the linked text to be tiny - and it would be if I crammed all 26 into the footer. This document is in portrait A5 format and is expected to be viewed on phones and tablets.

The viewer can always jump to ToC and choose any letter as all letters are entries in the ToC. I'm just trying to make it a little easier to navigate up and down the document.