Here is what I did to a Mazda 6 (?) seat. Any other foam seat is nearly identical in this regard.
The seat in question had side bolster foam separated and the metal support could be directly touched with manipulation of your shoulder blades.
LF seat, inner bolster was the worst. Very common for some cars in the entry level.
The issue:
Super77 spray glued the split foam back together, after letting it tack according to the instructions - you spray both parts to be mated together.
After you close the "seam", it needs some support to "smooth" things over and create a background of like color and keep things from digging into the seam again also. In this case the cover was split, not ideal but good luck finding another cover and delivering the car within a week of intake.
Gm presents a Grand Am production ... I cut up the covers from a Grand Am, because they conformed perfectly! Hurray for a spare seat in our upstairs off camera break room.
This was the final look, up close. If I could have used an iron on patch from the backside of the cloth, I would have.
There was a little waviness felt under the repair areas, but only because a small percentage of foam was missing or deformed from wear and this could not be avoided.
I sat in quikgt's re-foamed seats (denser material used - any upholstery shop will have access to the various densities), and it was night and day, a big difference in support and comfort - for the shape of the seat. This is not a racing inspired seat by any means. But at least Recaro got in on the Mitsu thing!