You have to remodel this. That's not how cushions insert into the base of the chair. The silhouette of it makes it look more like a pile of sand than a fluffy but wrapped around cushion. Also, I'd get normal maps done for this prop if you can. High poly to low poly bake. It's a decent start, but there's so much room to…
The silhouette and forms of the chair you made don't match the reference you have. That's what I mean by remodeling, or at least, editing the model you have now. Take a look at the cushion. Does it have the same silhouette as it does in yours? Yours admittedly doesn't feel like it was upholstered correctly. It just piles…