first, I'm not using it for sleep as I prefer the "softer" feel of shredded memory foam compared to sheets of memory foam.

I've got two king size polysleep pillows and I love them for the firm support they give when filled to capacity (with all the available sheets inside). I use them mainly for back support when sitting in the bed (Netflix sessions!). 

I've got 6 types of memory foam pillows and theses are the best for that purpose!