"There are different ways to construct the seat cushions. Most online stores have poly wrap around them. These will be more firm and will retain their shape well. If you like softer construction - you'll have to upgrade and look at a more custom furniture line.
It's a personal preference. What is great about design today is that even if you have a contemporary sofa - you don't have to have a contemporary space. And vice versa. You can mix and match to create a very personal and collected look.
Custom doesn't always mean extravagantly priced. There are a few places around that you can choose style/fabric/cushion comfort/frame color and not break the bank. Of course, people typically like the extras and it will cost a little more than buying something off the floor. However, at least you're getting something you really like and enjoy." Erika Barczak
Hope this helps when buying your next sofa!