I love alstroemeria - it is available in so many different colors, bi-colors and shades. It is long lasting and has several flower heads to a single stem.
You can see you can get a lot of design power out of a single stem. These flower heads hold up well in matching corsages and boutonnieres as well.
I clustered the alstroemeria heads in this bouquet because the mass has to balance out against the large lily heads.
Insert the flower heads as shown below.
Don't forget to tuck some of the flower heads deep into the center of the bouquet and under the lily flower heads.