Choose a sofa that has longevity and comfort. Springs support cushions best. Hand-tied springs are best; however, serpentine springs are also good. Test out the springs by trying to feel them through their upholstery. Look for springs that are close together and firm. https://tommynevins.com
Look for colors that will still look good in a few years from now. Brightly colored furniture can seem like a good idea at the time of your purchase but you will quickly get sick of it. Look for simple colors that can easily blend in different styles and decors.