You're Dr. probably removed your entire thyroid because of the size of your tumor (not because he thought it was malignant). My tumor was 2.2 cm and confined to my left lobe. So, my Dr. wanted to make sure it was malignant before she removed all of my thyroid. I wish I would have had it all removed at once. I hated having 2 surgeries.
The fact that your tumor was soft is a very good sign. Most malignant tumors are hard.
As for your scar, I don't know of any specific product that will help it to heal. My Dr. told me to wait awhile before I used any creams or lotion on it to prevent it from getting infected. My first scar looked pretty good, but after my 2nd surgery it doesn't look so great. I also have a lot of scar tissue behind it.
Radioactive Iodine (RAI) treatment (for thyroid cancer) is used after surgery to kill off any remaining thyroid tissue. It makes sure that thyroid cancer doesn't have a chance to develop anywhere else in the body and destroys it if it has. There is more information about this in the Information Archive on the 2nd page. I'll bump it up for you.
I hope this helps!