In my opinion one of the most sustainable choices you can make is to design and build your own custom furniture. Not only does this take much of the manufacturing process out of your furniture, it also lets you create the perfect piece for your space making you less likely to replace it in the future. In light of this idea, check out this great table tutorial!
Sylizimo's simple tutorial uses rustic wood and IKEA legs. Simple modern design doesn't have to be expensive and exclusive. You can make it yourself!