I would not buy those big armrests.
There is a very simple way to get much more steadyness in your fine motor movements.
You can experiment with a simple cardbox box, wich you put upside down on your desk.
Size of approx. 20cm by 30cm and a height of approx 15cm. (Or whatever size you prefer of course).
The idea is that you rest your elbows on the table, and your wrist on the side of the box. Then you have the work area on the top of the box. This technique is also used by people who do lots of fine mechanical work such as for example watch makers.
A cardbord box is great for the first experiments, and getting an idea of the size that works best for you, but it looks clumsy and ugly, and decreases desk space.
Making some table from a few pieces of plywood n the form of a big C will leave the front open, and increase desk space, instead of decreasing it.