In my many walks over the years, I've seen plenty of perennial beds that are over grown, full of weeds and just generally look a mess.. So, those need some maintenance also. Maybe even more so then a shrub perennial mix. Anything living that grows is going to need some tending to but a full perennial bed sounds to me like constant weeding and dead heading.

But to give any sort of recommendation or thoughts, it would be helpful to know at the very least what zone you live in and what kind of light the area gets, etc.

A photo would also be super helpful to see what is already growing and doing well there.

You need to add a picture(s) that show the overall space, but from close enough to clarify details. (May need to pivot camera taking overlapping pictures of larger space from not too far away.)

Also be so so careful of anything non native that promises to fill the in the area super fast with no work at all like Vica vine, ivy, snow on the mountain, etc. They are invasive and will be way more work in the long run, please please don't do it.

In my experience so far, anytime you add a whole new series of plants or shrubs, it is a process and a lot of work. That is also why a photo or an idea of what is already planted there would help. Perhaps there is a base already to work with that could just be tweaked a bit.

That being said I have seen some long term fill in success with day lilies or ferns. Sometimes hostas. They do take work to get established to that level though. Of course, I also have no idea if its appropriate for the climate, light and space you have going.