Garden Planting Plan

Just found this site and wonder if any of you knowledgable gardeners can help me.
I have started planting herbacious borders as designed by my local garden centre(over a year ago) and would like to change some parts of the plan but don't know what goes well next to one another.
I have one corner bed with two side beds. The corner bed is supposed to have a rowan and two birch trees. The side beds have clusters of rogersia, torch Lily, Butterfly Bush and Montbrettia.
I would like to change the trees in the corner for something smaller so I can still enjoy the views beyond the garden. Was thinking of rhododendrons but not sure.
Any ideas anyone?

 

Mmmm, one of the nice things about birches and rowans, is they are small and airy trees - rhododendrons will be evergreen and can be quite dark. If you want to change to something lower, how about the dogwoods, they have the advantage of colourful winter stems, as long as you cut them back.