2 layers; Froli and a serta topper that's 2 inches of dense foam and 1.5 inches of memory foam. amazingly comfortable. Our v berth is not set up to "sit" at, only sleep. doesn't even have the removable triangle in the front. That's where our water tank lives.
Don't see why you couldn't cut the foam to match the current cushions and replace the foam in them if it isnt comfy. the froli and the single layer of foam will be more than enough.
got it on overstock.com
ain't what ya do, it's the way that ya do it...