I'll have to look for those. The shoes that I had with the very low soles were a pair of Puma's. But I had to return them because the soles were falling off in just 2 months of wearing them. When I went back to the store to do an exchange they no longer had that style.
Oh by the way, when you do your good mornings do you do them the Olympic powerlifting way where you go on your toes as you thrust your hips foward to stand perfectly straight up?
Also, I know of the exercise you're talking about for the hamstrings. It's almost like a reverse leg curl if you will. Instead of your lower leg curling up, the lower leg stays stationary and the upper body from knees to torso and stay rigid and do the movement.
I used to do something similarly, but that didn't require a person to help you.
I'd use a lat pull down machine and a thin pole to help me back up and give me balance.
I'd start out by kneeling on the pad of the lat pull down machine, but I face "away" from it. So now the pad that normally is supporting and bracing the area of the thigh just above the knee (for lat pull downs of course) is now bracking the back of my Achilles tendon. I use the pole and keep it to one side of my torso and as I lower my upper legs and torso (all kept rigid and in perfect line) I would use one hand/arm to press the pole into the ground to help give me support as I become perfectly horizontal with the floor. I'm face down and then I raise myself back up. I only use the bar with my hand/arm as much as necessary to help me get my body up. At first you feel like you'll never be able to do it. But then after a few weeks you can do it without hardly using the bar.
I like Nathan's method better, but at least my method is good when you don't have a training partner to help you out.