Roses are a bit of a cliche, but you might get away with it as long as you don't send red ones. Why not try doing a bit of research into the meaning of flowers - you may find that another, more interesting flower might say what you want to!
Oh, and another bit of advice, if you must do the flower thing, loads of one sort and in one colour always looks more generous and stylish than a mixed bunch or arrangement - even if it's onlt ten bunches of daffs! Trust me on this - me and my sis do loads of flowers, and we know!