looking at changing my fork oil on my 2012 fatbob seems to be diving a bit anyone got any pointers thanks in advance!

On my lowered '08 Fat Boy, I changed from the standard 10 wgt to Screamin Eagle 15 wgt. Gives a little more cushion without stiffness and I've been comfortable with it for 5 years.

 

Progressive springs and SE heavy weight oil firmed up the front on my '03 Dyna, it made a helluva difference.
Roo.

I replaced the standard springs with Progressive Suspension 11-1525 springs. It has made an improvement but still not exactly what I was aiming for. Still a little too soft for my personal taste.
I would suggest if you were looking at changing your springs go the 11-1526 or the Monotube cartridge type. Haven't messed with the oil viscosity yet.