While the exact number will depend on the size of your sofa or chair, the general rule of thumb is to use an odd number of pillows whenever possible. For instance, you could place a single eye-catching lumbar pillow in the center of a sofa, and then add a pillow on each end for a smaller sofa or two on each end for a longer sofa. Whether the pillows are all the same size and shape are up to you – don’t be afraid to experiment!