A manufacturer or upholsterer who is experienced in working with faux leather - whether its polyurethane, PVC or Semi-PU - knows that what's underneath is as important as what's on top. They'll only use a top quality, high density foam. Density is considered to be the most important indicator of overall foam quality. Density is measured as the weight of a cubic foot of foam. High density foam is less likely to “bottom out”, “fatigue” or “dish.” High density foam cores can be designed to provide plush surface softness without sacrificing deep-down support.
The upholsterer will overcut the foam in both directions so that all corners and frame surfaces are well-covered. They might suggest wrapping the foam with a backing fabric so that the foam "recovers" more quickly when someone sits on it. The way your faux leather is sewn can mean the difference between long furniture life and a quick "field failure." Tight folding around corners, without the cushion of foam, will stress the faux leather, making the top film layer susceptible to tearing, picking and breaking.
Double-stitching any seam that carries a lot of stress can be a good idea - but stitching back and forth over the same line could simply cut the top film. A maximum of six stitches per inch is widely accepted as good practice (more stitches may tear the fabric), and using a light ball-tip needle is the way to go. Nylon sewing thread is typically used for indoor furniture while polyester thread is recommended for outdoor furniture.
And one more thing that an experienced manufacturer or upholsterer will know: welt cord on coated fabrics spells trouble, especially if the welt cord is in an exposed, high abrasion area such as a cushion top. Think about it - you're taking a piece of fabric with a top film and wrapping it tightly around a hard plastic tube, and then you're subjecting it to continual rubbing as people sit down and get up, sit down and get up. Welt cord creates greater tension which reduces the flexibility of any type of faux leather, making it easier to abrade the surface of the material. So, stay away from welt cord.