I'm the last person you should listen to for aesthetic advice!
I'm a total nerd-engineer so I like square corners.
Shallow terraces, perhaps edged with a single row of bricks or small stones would appeal to my graph-paper aesthetic. Maybe just a row or semi-circle of stones down-slope from each bush so that its little patch of soil and mulch would be level.
If you wanted to level off the entire
slope, much better to do that with 3-5 terraces, each 3-4 feet wide, with paths between them 2-3 feet wide. That way, the path that you walk in could be dead-level and the soil surface in the beds could be level. The "up-down" pathways could either remain the current gentle slope or be "stair-cased" and supplied with paving stones laid flat.
Each "terrace" or partly raised bed could have a 6-12" wall along its bottom edge (and maybe nothing on its upper edge).
One nice thing about narrow beds running along a slope is that you never need to shovel farther than around half the width of the terrace, and you only need to change the depth by at most 1/2 the height of each terrace "step". And you can throw the topsoil from each path onto the bed, doubling the depth of the good-soil root zone.
Since you only need shallow "steps" and not a strong retaining wall, maybe just treated boards would be enough to edge them: like 6", 8" or 10" boards.
I like concrete paving stones set on edge and leaning "in" a little. They are cheaoer than wood, unless youget a real bargain on wood!
The 1" thick kind, 12"x12", look more solid and can give you a 12" wall if you want it that high. My second JPG shows some 12" square pavers in the background. Solid.
The 3/4" thick pavers are 8"x16" and hence cheaper if you run them the "long" way. You can use those either way: 8" wall or 16" wall, but I've started to think that the 16" wall doesn't look as cottagey as lower walls. My first, 4th, 5th and 6th JPGs show the 8x16" pavers used the long way: informal and friendly.
I stood some 8x16" pavers up the tall way in JPG #2 foreground. Those do need to lean in a little more, for stability, and I adjust them every few years (or I should, to keep them tidy).
You can get these pavers in a neutral light gray color. You can paint either kind, for example with a roller. Maybe match the color of your siding, to tie the beds to the home.
It might even look nice if you gave the beds a gentle curve along the contour.
Oh, yes. You need to allow for drainage unless your subsoil already drains well. A few slit trenches running through
and under the beds, filled with gravel or a plastic pipe, so that heavy rain runoff doesn't have to perk through each bed, one by one, to reach the bottom of the hill.
Or "herringbone" the beds and paths at a moderate angle to the slope, so that a downpour would be guided to the central up-and-down path or stairwell, and then straight downhill.
These are the closest examples I could find online, but I was picturing walkways between each bed. Bear in mind that this website SHOULD be named "Expensive Homes and Gardens"
page 4 Cor-Ten raised beds
p. 6 Las Villas
p. 8 Nature's Beauty
p. 11 Monroe House & Alfresco Living
My untidy, geeky versions are:
I barely started this staircase before I was distracted: