New Sleeper Beds, What To Fill With

Hi, first post on this forum and new to gardening.
We have not long had 3 sleeper beds built, which will be in full sun, approx 80cm deep.
We ideally would like to try and cover the fences and trellis using the 2 big beds, have some height at the back etc and full of colour.
The middle sleeper we will use for bedding plants through the different seasons again for colour.
We just don’t know where to start, especially with what will cover the trellis in full sumacs then what to go with it.
Any ideas are welcome, many thanks.