You need to understand that a "portrait" lens, depends . . .
. . . on what KIND of portrature you shoot, and how far from the subject you are.
A 10 person family portrait in a small studio may require a wide angle lens, say 35mm.
A "tight" face portrait a mid to longish range tele, say 200mm.
And everything in between.
Back in the film days, the standard Nikon head and shoulders portrait lens was the 105.
Today it seems the standard choice is the 24-70/2.8 and 70-200/2.8 pair. But those are pricey lenses.
A good alternative is something like the Tamron 35-150/2.8-4.
ONE lens, vs. two.
From moderate wide (for group shots) to moderate long (for the tight face shots).
Not the WIDE aperture and shallow DoF of the 85/1.8, but more flexible.
I would sit down and look at your prior pics with an editor that can read the EXIF data.
Then determine what focal length you seem to shoot at the most.
Multiply that by 1.5, and you have your FF/FX equivalent lens.
Example 50mm x 1.5 = 75mm
This is most useful with pics that you shot with your zoom, as you would be zooming to the focal length you need for the shot. vs. a prime lens when you just have to "make do."