SkechersWomen's Keepsakes-Ice Angel. Sweater Slipper with Plush Foam, 4

Is the back high enough that they don't slip off the foot?

I have hardware in my foot, and I need a very thick comfortable pad so I don't feel it. Is this very thick?

What material is on the inside of these slippers?? Is it super soft?

Are these slippers stretchy? The outsde knit material looks like it could be.