You’ll rotate that mattress, not flip it.
Regular rotation will give you more even wear, as the years go by, resulting in greater longevity.
That particular mattress is comfortable for most people in any sleeping position.
I recommend waiting about a week after you receive it, to determine if you need a topper to soften it further.
It takes about a week or so for a new mattress to loosen up a bit. It’s a little stiff, at first.
It also takes about the same time for your body to get used to its new home.
(So to speak).
An additional mattress topper may or may not be necessary.
So, it makes more sense to wait.