... have to do surgery on my new Englander "Malibu Firm"?

Here's the deal: I  never could get specs on the foam inside my model, but the Plush version of it had 5, count 'em, FIVE inches of cheap polyurethane foam. I'm guessing this one must have at least 3½ or 4" of cheap pu foam on top of the springs, fiber, etc.

So... here's the report so far: (remember I never bought it based on thinking it was going to work out as is, I planned from the beginning to do surgery on it):

1st night:
Better than my foam, but too hard.

2nd night:
I added 1" of venus foam on top of the mattress.
Got the best night's sleep I've had in probably a year. Usually I wake up after about 6-7 hours with my back KILLING me and even though I'm sleepy and groggy, I HAVE to get up because my back hurts too bad to remain lying in bed.

Slept a good solid 9 hours and still did not hurt too bad. That is to say, yes my back did hurt, as always, when I got out of bed, but I'd say it hurt only about 15-20% of what it has been hurting the past year.

So, my question is, when will this new mattress start breaking in to the point where it hurts my back and I have to open it up and begin replacing the foam with my own HR and latex etc.? a week? a month? 2 months? 4 months?

I don't have a prize to give to the winner but you'll gain the title of Best Mattress Diviner or something...

My guess is that it will begin breaking down in about 2 weeks and I'll wait a suitable period to make sure it isn't "just me" and so will cut it open in about 3 weeks...

I hope I'm wrong!  I hope it gives me great sleep for at least 6 months. Hell if it does I might just buy a new one every 6 months!