I got a suggested layer stack, and and it makes mention of "edge coupled offset stripline" and "edge coupled coated microstrip".
Are edge coupled traces differential pair traces or are they any adjacent signal traces ?
The edge coupled offset stripline is a closely coupled diff pair on an internal layer but offset to be very close to one plane. So maybe layer three for you close to the plane on layer two, as opposed to being in the middle of two plane layers
The edge coupled microstrip is a closely coupled differential pair on an external (too or bottom) layer.