Welcome! Please take a moment to fill in more of your profile info. Details like your zone help a lot in determining what plants will be suitable.
In addition to the plant height you desire, it is also important to know the depth of your shelves, the depth of your pond, and if you plan on keeping the plants in pots, or adding large rocks for the plants to grow in. Will you be adding fish or other live animals? Are you looking for grasses or bushy plants? Do you only want plants in the water, do you want to include some in the rocks, and are you interesting in plants that grow from the rocks and hang into the water? Do you want green plants, red plants, yellow plants, flowering plants? That's one of the great things about pond... there is such a huge diversity of plants available, you can find something to fill every niche, and in a few years your pond may look nothing like you originally envisioned it but it will still be exactly what you hoped for.
So to get started... I see you are in England, so your growing zone is probably between 4 and 6? You can do tropical plants, but you will need to take them inside each Winter -- it's easier to start off with perrenials. Most people will start with a lily -- easy to grow, and they get put in the bottom of your pond. The leaves provide cover for any fish, and the flowers are fantastic. Tall grasses are also easy, and really make it feel more like a pond. Corkscrew grasses are common, but their roots really need to be kept at less than 15cm (water depth). There is also zebra grass, with is thin and can get up to 120cm -- it does fairly well at depths up to 30cm. There are various rushes and umbrella plants which get bushy. There is ground cover such as moneywort (creeping jenny) which can cover your rocks, grow down into the water, comes in both yellow and deep green, and gets small yellow flowers. There are various mosses you can grow in the rocks. And there are irises, which can be grown in the water or in the ground.
Hope that's a helpful start? Give us some more details, and someone will come up with just the right plant for every spot you have.
