Trust me, you won't want to wear an underwire for quite some time - it will be very uncomfortable. It's been a year since I had mine done, and I still don't like to wear an underwire - I wear sports bras almost exclusively now. (Before I got the implants, I used to wear nothing but underwires, and everything else felt uncomfortable to me.)
You'll probably be wrapped in ace bandage for the first 24 hours, then they will see you to remove stitches and take off the ace bandage. At that point, my doctor provided the sports bra that you have to wear for the next month or so. Also, there is the "bandera" which is a sortof ace-bandage like strap that wraps around your upper chest and velcro's in the middle. It is supposed to encourage your implants to "drop."
I had lots of pain for a long time, even though I went above the muscle. Not sure how much of it was due to the incision site - I went through the belly-button. I was very happy with the end results, though, no scarring at all. Other people go below the muscle (which is supposed to hurt more than above) and are pain free in a few days. I think it depends on the individual. But the good news is: your doctor is there to make sure you are okay. If you have lots of pain, tell him/her! They will ensure that everything is normal, and prescribe more pain meds if needed.
In a few months you will be lovin' your new look!
Take care,
Fennec