Hello Bell,
The best thing for topary trees is ming fern. alternatively have you got any foliage in your garden like viburnum or eunonymous, never can spell or say that one! Try putting your cones on a low heat in the oven for an hour or two, they only open when they are dry. If you ever need closed ones put them into warm water for few hours and they close again - clever little things!
Good luck with your assesment.
Breezy
