Hubby and I have finally been able to spend a couple of nights on the boat. The new mattress is terrific.  It fits snubbly into the berth so there are no odd gaps in the middle.  It is both firm and forgiving so old joints are not stiff and sore in the morning.  The finally verdict is using an IKEA foam mattress to make a v berth mattress works!

Next winter we have to consider redoing at least the covers on most of the rest of the interior cushions and redoing the Port berth cushion.