Great article. I think there are some flaws but it gives lots of good ideas.

Possible flaws:

• Insulating the underside of the work surface would prevent the work surface itself from getting warm. Hands have the most need for warmth. So I would be tempted to insulate the underside of the work surface as suggested but cut out a deliberate thermal bridge around the keyboard and mouse area – or maybe supplement a heating pad on top of the desk.
• Space heaters are discouraged because they output too much power (as they are intended for heating a small room). But space heaters often have thermostats. I have an a/c powered oil radiator on wheels. It may be high wattage but I think it will know when to quit.
• IIUC, they rely on the blanket to mitigate heat loss around the sides of the desk. That’s where I would be tempted to use insulating radiator foil, perhaps in addition to a blanket.

Thick insulation foam for roofing is often thrown out, like when a neighbor re-roofs and buys too much. I will be on the look out for scrap pieces to use under the desk.