OK, so if you are say in Springfield, you are right on the border between (cold hardiness) zone 5b and 6a:
https://climateillinois.files.wordpress ... edium1.jpg
That just tells you how cold your winters typically get, so how cold hardy your plants need to be. Since plant roots are a bit more exposed on a berm, I would look for plants that are hardy to zone 5. Sorry I had missed where you said it is full sun.
For your ornamental trees, I recommend serviceberry or viburnum. Both of them come in a variety of sizes including dwarf and both of them have berries that birds like. The serviceberry has edible berries, which you can make jelly of if the birds leave any and there are 40 different kinds of birds that like them. Viburnum is attractive to somewhat fewer kinds of birds, but it is still a good habitat plant AND its flowers are incredibly fragrant, perfume the whole yard while it is blooming. Both are kind of shrubby, but can be shaped as trees if you want. They are native, so will be very hardy and low maintenance, once established. For actual trees, redbud or dogwood are beautiful small trees. For foliage color, you can add a dwarf Japanese maple. Or for native small trees/large shrubs with colorful foliage, there is purple ninebark, black lace elderberry, smokebush.
Or you could use 'wine and roses' weigela as a shrub to provide foliage color while stepping down in height. They say it gets 5' tall and 5' wide, but the one I had in a part shade location stayed smaller than that. And there is a more compact variety called 'fine wine' that stays under 4' tall.
Red twig dogwood is a nice deciduous shrub for winter interest. After it drops its leaves, it shows bright red stems that are gorgeous in a snowy landscape. Artemisia (called white sage or silver sage) is a nice low shrub, that grows in a mound, and has silver leaves, that are a good contrast to other plants. It is aromatic, has medicinal uses, and is very tough and hardy.
For something evergreen kinnikinnik/ bearberry is a very pretty, low growing, trailing native evergreen with pretty flowers that are attractive to butterflies, that become bright red berries that birds like. If you are going to add some rocks/boulders to your berm, the bearberry is beautiful growing over them:
https://www.wildflower.org/image_archiv ... MG0165.JPG
kalmia / mountain laurel is a much under used native broad leaf evergreen shrub, with beautiful flowers. The hybrid varieties come in a range of sizes from large-ish shrubs to very small.
wayside gardens (waysidegardens.com) is one catalog that would carry many of these. Definitely not the cheapest place to buy from, but very high quality, well started plants.
Do be sure you think about how your berm will look through the seasons. Here's a post I wrote about 4 season gardens:
https://www.helpfulgardener.com/forum/vi ... hp?t=35084
Hope this gave you some ideas to start with. I didn't say anything about perennials, because the trees and shrubs will give the structure to your new bed. After those are planted, you cans see what the space looks like and fill in with perennials. Have fun planning through the winter! Let us know what you decide on and how it looks! We love to see before-during-after pictures of garden projects.