Hello. I'm truly sorry you are going through this. I had to stop feeding my DS2 at 16months. I had two weeks to do it. I too exhausted every avenue and there was absolutely no choice for me.
As far as I can recall this is what I did.
Stage 1 - stop all feeds "during the day" leaving bed time, nap time and wake up. Start limiting other feeds but don't end completely. Ensure dressed all the time in inaccessible clothes. Change daily routine/activities to signal change afoot generally.
Stage 2 - arrange life around falling to sleep for nap by other means every time - car, pushchair, sling.
Stage 3 - drop wake up feed, and zoom off downstairs with Daddy for breakfast fun on waking.
Stage 4 - drop bedtime feed.
Stage 5 - drink shedloads of sage and peppermint tea. Sage helped dry up milk, peppermint to cool any engorgement.
Stage 6 - keep breasts hidden and inaccessible for a while.
I was truly traumatised by all of this but my son was absolutely fine, and I had no engorgement or breast problems.
I talked to my son about what was happening and why. I can't imagine he understood everything I said but I'm sure he understood the main thrust of "no more mummy milk".
Oh, and be careful who you talk to about this IRL. I was about to sob on one friend about how sad I was about having to give up and she revealed that she'd cried every day until her son was one because she had been unable to breastfeed him. Make sure you're not going to traumatise your friends too!