I had to wean my son when he was 14 months old because I was starting on a medication that was not studied in breastfeeding.  At that point he was down to, I think, 3 feeds a day - before each nap and before bedtime.   

If there is no hurry I would say to cut out a feed at a time maybe, say, a week at a time...  but we were kind of in a hurry.  So for 2-3 days I gave him a bottle before his morning nap, but nursed before afternoon nap and bedtime.  Then I cut out the afternoon feed.  Then, finally, the bed feed.  Sometimes I gave him water, sometimes I gave him milk in the bottle.  I just gave him the bottle and rocked a while and then put him in bed.  Eventually we just rocked before sleep, no bottle.  It went much easier than I expected it to.  I was actually kind of insulted that he didn't fuss more about it, LOL.

I had porn star boobs for maybe 3-4 days...  then for maybe a month more I had milk if I tried to express it but it wasn't a discomfort to me.

I don't think the degree to which you sag afterwards has anything to do with how fast or slow you wean.  I think it's just a fact of life that everything is subject to be re-arranged after pregnancy and nursing.  A good bra may ensure you don't have the sagging any worse than you need to, but it's not going to prevent it altogether.

"Gravity always wins."

Luck and genetics play a part, too.

FWIW my boobs look no different now than they did before I had my son...  but they weren't really anything to write home about before, either. 

I nursed all mine for around about 2 yrs (think 12 yrs of pregnancy, nursing or both without a break).  Until they were 1, I insisted that they nurse, no matter what they were or were not eating otherwise.  It was a good insurance policy for their health, I felt and I believe I was right.  After they were a year, I didn't invite them or insist.  They were always in the morning, always at night and literally, on demand because if they wanted to, they had to do the asking during the day. I just stopped instigating nursing and it took a year before they got to where they stopped asking.

As for drying up...after 12 solid years of it, I think my youngest was 6 nearly 7 before I finally dried up.  It took 5 yrs.  Then again, when you use your body as a human cow for 12 straight years, it doesn't know how not to be that way, I suppose. 

For the record, I know what causes pregnancy and just because I have 6 doesn't mean I didn't know how to stop it happening.  If I didn't know, I'd have 12 not 6!  There are people who consider children a luxury, I considered them a necessity.