Hi.
Small ponds are a pain. There's such a diversity of things that seem to want to be there that it's near impossible to keep them all happy. There's also the problem of the ever expanding roots of your water plants, which before long hardly leave any room for water. My own pond is about the same size as yours and I need two or three buckets of dechlorinating water at the side in summer. It sounds as though you've already bought a pre-formed liner. These usually have two or three different levels built in, to accommodate various types of plant. If yours hasn't, a few different sized stones will do the trick. I've never seen this done, but would a seed tray full of granite chips, standing on some stones and barely submerged do the trick to emulate a shallow end? The trouble is, each time you put something else in there, more water is displaced. Fwiw, I have part of an old roofing slate leaning up against one side, which makes it easy for very small frogs to get out, and the underside provides some shade for the adults on the hottest (?) days.
Hope you're successful.
Geoff.