Ok update!  
I found small “no slip” rug pads at the dollar store. (You could buy one big one and cut it up). It keeps the cushions in place!
Next, I bought rubber pads for the feet. Now the set stays put!  Note to sellers - these items cost less than 10. Just include them!  

This is super comfy, with great quality slip covers. I searched for a high-back, low arm sofa and this was it. The plastic rattan material is large weave and smooth, not rough like some. 
My only complaint is the pieces have no attachment to stick together. They slide around on my tile lanai. I’ll fix that with Velcro, but paying 900 for a sofa, you’d think they’d do that for you