Lavender is typically harvested just before the flower buds open if that is helpful to know. But I understand the sensitive nature of allergies too.

Another thought would be maybe some lavender essential oil, which is not too hard to find a natural market or health food store, or online.
A little dab on a piece of cloth or cotton ball would probably work as well as the flowers.
Something else I thought of too- white noise in the background. You know, like those hokie "lull you to sleep" music cd's or special radios that play beach waves, babbling streams... etc that were really popular about 10 years ago.I have some cds like that and when I used them it was helpful.
Now, I usually have either a space heater going in the winter, or a fan in the summer. The seady hum in the background seems to help me drain my mind and sleep better.
Whenever the weather is in the spring or fall in-between stage of not really needing either, I find it harder to fall asleep. It is
too quiet in the house. Doesn't matter how noisy it is outside, if it is too quiet
in the house I can hear my thoughts bouncing around in my head.
I have a tiny tabletop personal fan I will actually turn on, but facing away so I don't get cold just to have the quiet hum.