The comfy sofa you tested in the showroom may not feel like the same couch that gets delivered to your home. The couch at the store had the benefit of being broken in by many shoppers, while your new furniture feels stiff to the touch. The cushions on your couch will soften over time, but if you want to speed up the process, try a few tactics to compress the foam insert and loosen its fibers.
In addition those sofas which are made with premium leather being a natural product, may also be slightly stiffer initially. This is because its brand new and will become totally pliable after some usage. This is combined with the foam relaxing after some days.
Lay a thick comforter on the couch as you wait for the cushions to break in. The comforter will act like a pillow top and provide some softness.
Be careful when bouncing or walking on your cushions. Certain materials, such as leather, can rip easily if handled too forcefully.