Mary,
First, to add to your confidence about using M over Av, just remember that all you're doing in M over Av is setting two items instead of one. As Donald pointed out that Colin pointed out
the camera tells you what it would have set the second setting to, so if you're comfortable setting the first (aperture), then reading what the camera is telling you on the exposure meter scale and setting the second variable should be no problem. You can definitely do it!
Also, as Donald points out, you can use ISO as the third variable to help you out. Recently, with my flower photos, I've been fighting the same issue you are having with the wind. To help counter balance that, I'm setting my shutter speed up around 1/125 at a minimum, but leaning towards 1/200 or 1/250. When I had the camera set to ISO 200, it would suggest 1/40 for my shutter speed, and that was too slow to eliminate the movement caused by the wind. I flipped to ISO Auto mode, and found that it was quite happy with only bumping up to ISO 400 for a lot of the shots.
Granted that does nothing to help when the wind movement is enough to move my subject completely out of my frame with the macro stuff I've been doing, but it does help when things do line up.
However, one thing you can console yourself with is the fact that a tripod would
not help at all. If your subject is moving, the only thing that is going to help is a faster shutter speed. In fact, a tripod might actually make things worse! With handheld, you could actually compensate a little for the movement caused by the wind - though it'd be really hard.
Go to M and set your preferred shutter speed and aperture, and see what Auto ISO mode does for you.
- Bill