Seats and foam are 2 separate parts and can be bought separately. I'm guessing if you foam is moves and separating it is probably because your seat back spring has broken and you are sinking further into the seat. This was common at least in the 2010.
I would have to take the seat out but it might not be necessary. The seat comes our really easy though and makes the job supper simple. There is 2 very large Torx screws in the back of the seat connecting it to the track, the front is just hooked on so when you remove the back bolts, slide the seat back an inch to clear the hooks and disconnect the power harness and it's out.
If the foam has been bad for a while you probably have bad wear in the seat cover in the spot that the metal bar is so you may want to replace that while it is all out of the car it is really easy.
Here is the link for a 2010, I'd re-run this search for a 2012 just in case there have been any changes. If you just change the back spring (assuming it's broken) and the foam it'll cost you about $120 from this site with genuine GM parts. Parts # 4 and 6
https://www.gmpartsdirect.com/auto-p...wer-seats-scat