If you can see the boot actually moving in and out, you've got play
elsewhere. If the bearing were bad, the most you'd get would be some
rocking of the shaft-- it wouldn't move in and out. I'd also expect you
to have one heck of a humming or rumbling noise when you drive.
The top of the wheel is pretty much fixed in place and won't move due to
the strut attachment. With the wheel jacked off the ground, grab the
bottom and see if you can pull it in and out. If you can, the problem is
likely in the ball joint. Look specifically to see if the control arm
pushes up and down when you move the bottom of the wheel in and out.
Similarly, when you rock the wheel from side to side, you should be able
to see the tie rod end joint move if that's where the issue is.