A grown Labrador is usually 55 to 80 lbs and measures roughly 36 to 40 inches from nose to the base of the tail. That's a lot of dog pressing down on the same hips and elbows for a decade.
Labs are one of the breeds most commonly affected by hip and elbow dysplasia, and many develop arthritis as they age. None of that is a certainty for your dog, but it's common enough that it's worth planning for. A worn-out or flat bed lets a heavy Lab press straight through to the floor, which is exactly what you don't want once the joints are already sore.
Egg-crate orthopedic foam spreads that weight across the whole bed instead of concentrating it under the hips and shoulders. In practice, the difference shows up in the morning, in whether she springs up or hauls herself up.
One more Lab-specific thing: they shed, they swim, and they bring the outside in. A cover that actually unzips and washes is not a luxury with this breed.