I often recommend that patients sleep with their backs elevated after many of my surgeries. This helps reduce swelling, especially for face and eyelid lifts. For breast and tummy tucks, this position improves comfort initially by maintaining a partially upright position so getting up is easier. It also reduces tension for abdominal operations.
After a week or so, it is usually fine to resume sleeping in bed. For side sleepers after breast surgery, I recommend hugging a pillow to act as a cushion against pressure from your arms or your bed. For stomach sleepers, you should not resume that position until at least six weeks after surgery.
Of course, please feel free to ask if you have any questions.