I am looking at buying a BY sofa in grade 5 leather. Which seat cushion is recommended: HR foam, spring down, or premier down? Are the cushions replaceable at some point down the road?

I have the BY Melbourne sofa with the premier down seat cushion. It is comfy but there is some puddling of the cushion that gets the most use. I've had it 1 year.

The H&M Arrington sofa that I sat on in the store was by far the most comfy cushion I've ever sat on. I believe it was the H&M standard cushion.