However, if it is severe, then you will need to do a breast lift with the augmentation. I believe what you mean by a watermelon look is a breast that is somewhat conish in appearance, or it can also mean that you have the edges of the implants show significantly. A good way to avoid this problem is to not be too over-augmented and not force the surgeon to put in too much of an implant for that particular chest. In other patients, their natural breast shape is a cone and special maneuvers must be under taken to fix this problem. No, saline implants do not feel more natural than silicone.
Silicone implants feel more nature than saline implants.
Not all surgeons require mammograms prior to surgery. However, most require a mammogram within a year prior to surgery. I do not personally require one prior to surgery if they have had one within a year. There is no way to enter or insert an implant without creating a scar. With saline implants since the implants can be completely deflated before inserting them, fairly small incisions can be made.