Last spring, I decided to add this rattan dining set, which has been awesome for morning coffees and outdoor dinners. I've accessorized it with some outdoor cushions for extra comfort and a couple of potted plants on the table for a bit of character. For the rest of the garden, I added a small bench in another corner, which doubles as extra seating and a decorative piece.
Since your garden is 20 square meters, I recommend measuring out your space first and taping down the approximate sizes of the furniture on the ground, just to make sure everything fits before you purchase. It can be tricky to eyeball it, and you want to make sure there's enough room to move around comfortably.