I would use the smaller, alpine campanulas that you can get from the garden centers. Wait until late spring or early summer and see them in flower in the GC, there are many named cultivars to choose from. Maybe a mixture of blue shades to line a path?

thanks

Edging a path for flowering earlier in the year. ie. springtime, you can use Aubrieta..

It may help you to look at GoYpedia Campanulas...
click on C at the base of this page...
and GoYpedia Aubrieta...
click on A at the base of this page.

I hope this helps :o)

Campanula muralis