I was going to order parts to build a 2nd device, so I can have a keyboard in my left hand (Spacebar, Enter, Escape and Backspace), and a mouse in my right hand (Left-click, Right-click, Wheel scroll up, Wheel scroll down).

But it looks like the DRV5053VAQDBZR magnetic sensor that I used is currently out of stock at Digikey, Mouse, Farnell / Element14 and various other distributors! It looks like they won't be back in stock for a few months. Luckily the manufacturer Texas Instruments in USA still has several thousand left in stock, and TI is willing to sell them in packs of 5 sensors for $4.80 with free shipping to various countries.

So if you are having trouble finding these specific magnetic sensors, try

https://store.ti.com/DRV5053VAQDBZRQ1.aspx

If TI stops producing this sensor one day, there are a few other magnetic sensors with similar sensitivity that should work OK as a replacement.