I am using an LG 5K monitor, and the display scaling options are very limited in gnome-shell, only increments of 100%.

To have fractional scaling, I tried this script:

#!/bin/bash 

gsettings set org.gnome.desktop.interface scaling-factor 2
gsettings set org.gnome.settings-daemon.plugins.xsettings overrides "{'Gdk/WindowScalingFactor': <2>}" 
xrandr --output DP-1 --scale $1x$1

I added that in a script inside /usr/bin/scale_me_please.sh and make it executable:

sudo chmod +x /usr/bin/scale_me_please.sh

Now, whenever I am at work and need to scale it, I just run:

scale_me_please.sh 1.4

Just perfect!

Update: This change has introduced some screen tearing for me on Intel graphics. The solution was to add the following:

Section "Device"

  Identifier  "Intel Graphics"

  Driver      "intel"

  Option      "TearFree" "true"

EndSection

To /etc/X11/xorg.conf.d/20-intel.conf

For some reason, this changed my display from DP-1 to DP1, so I modified my script replacing the former with the latter.

Enjoy!

Sources:

https://wiki.archlinux.org/index.php/Intel_graphics#Tearing

https://askubuntu.com/questions/1029436/enable-fractional-scaling-for-ubuntu-18-04