Advice for physics movement

I'm trying to make a very abstract physics platformer with rigidbody movement. You essentially play as a wheel dolly. You know, those square platforms with wheels designed to move around trashcan and the like?

Anyway, so the ideal is that you can roll around, jump and flip onto your back, and continue rolling around on your back. I've already got the jump and flipping physics all taken care of.
However, even though I used a zero-friction physics texture on my rigidbody object, my player object can only move horizontally while in midair. I think because my object is a rectangular prism rather than a sphere, the friction is way stronger than it is in any of the physics tutorials.

What would you recommend as the best way to get this rigidbody to slide around on the ground via physics?

 

I'm not sure I understand, you mean on of those big trash can with wheels on it?

How is your current controls set up? without knowledge of this we can't exactly tell you what's wrong/missing.
What do you mean a 'rectangular prism'? I imagine you mean you can move 'upright' and 'on your back', if you have the wheels you should be able to do both, more information on your setup is needed.

 

Oh no, not a trash can, one of... actually I'll just post an image. Though instead of wheels, I'm going to have spheres tall enough to protrude above and below the base plate.

And I don't have wheels, I actually wasn't sure if that's the way to do this. Wouldn't wheels have too many constrictions on them? I want the controls to be reliable as possible. I'm not familiar with how wheels work in unity, but I suspect they're a little more complex than what I need for my project.

As for the rectangular prism, it's basically a flattened cube (I'll make a more detailed model later) with a rigidbody on it. I move it by applying physics forces.