I don't think the brand is super important; they should all be pretty much the same. I used to have some big name brand (though I can't remember which one) back when I was a kid, but when I accidentally ruined my pillow, I replaced it with this six years ago:
I can't really tell the difference. The main things I would look out for are the amount of filling and whether or not it has a zipper. If the pillow isn't full enough, it's going to suck and you'll have to get more buckwheat. If it's too full, you can simply dump some out. That's the nice thing about having a zipper. You'll also want one for cleaning purposes. You can't throw one of these suckers into a washing machine. You need to pour the buckwheat into a container and set it out in the sun for a few hours. Meanwhile, you can vacuum out the inside of the pillow case (to remove any debris) and then throw it in the wash.
They can easily be found on Amazon. I've been using THIS ONE for the last six years.
I am due one day after you and am having similar issues. Two things have helped:
Also, if I go more than two nights without at least three hours, I take unisom, which has been approved by my OB.