All you need is a large enough surface area to accommodate what you need at hand—for most people, a laptop. It can be as little as 20 inches (or less) deep and as wide as you have room for along an unused stretch of wall. If you prefer less furniture, double up your mini desk as a side table!
Here the Desky Single Sit Stand Pedestal Desk fits the bill perfectly at a square size of 600mm x 600mm that will suit any office nook. It lifts up to 50kg and has three pre-programmable heights.