My 2009 Suzuki SX4 had those narrow little arm rests, for both the driver and passenger.
I made a padded arm rest that just sat on top of those wimpy little rests.
That arm rest was/is Keystone shaped, wider at the front than at the back, so it just jammed in between the seats and worked great for both the driver and the passenger. Both seat-backs had to be set the same.
Then for the Kia Soul, with NO arm rests at all, I had to make a bracket, that would hold the arm rest.

It's upside down, sitting on my work table.
Once installed it looks like this:
'
The turned dowell sits in the little junk tray. The top is hinged and adjustable for comfort.
Just one screw at the bottom of the long board, holds the assembly to the back of the center console.
It fits snugly between the seats and side movement is negligible.
Cost? $00.00, all made from scrap materials.
Just a little DIY project for a sunny afternoon.
Cheers Mates!
Other points of interest, the Seat Belt Extender, to make buckling up a SNAP!

Steering wheel cover to prevent hands sweating on the plastic wheel, and of course,
the obligatory cup of Dunkin' Donuts coffee.