Let's start this design by placing foam into the container. The larkspur is tall and impressive. Next, let's create some contrast in shape.
Larkspur is a very flat, spikey kind of flower.
Notice how we are gradually working down and towards the left, filling in the baseline with our roses. Thus the roses are placed quite flat, in towards the baseline. A little bit of statice now provides even more contrast to the mixture. Very little foliage or moss is likely to be needed because the flowers themselves are packed in closely enough to the base to provide a great degree of cover to the mechanics. For a significant other.