I'm still BFing my 20 month old. Mostly at bedtime and if/when he wakes in the night. He will, when tired, climb into my lap and pull at my clothes, and my husband has said that sometimes he gets into our bed and lifts my top up while I sleep straight through it!
He will only feed on the left one too, which makes me somewhat lopsided, but that's ok, they've never matched anyway.
I rarely do it out and about these days, unless he hurts himself or is particularly tired or upset. He is easy to soothe without the boob, by me or anyone else. He is looked after 3 days a week by grandparents and has never tugged at their tops, so knows that it's me and only me that provides that particular comfort!
If I'm out, he will take a bottle of cows milk at bedtime, although not very much, but will usually go off to sleep as happy as Larry.
I will stop when he stops. I don't do it for me, although I have to admit I do like the downtime it gives me - feeding him for half an hour at bedtime gives me half an hour to read/rest or whatever, and to appreciate cuddles with my little boy. He is soooo cuddly, and I am too busy so much of the time, that yes, that part of it is for me. But I wouldn't keep it going just for that - I don't even know if that is possible, can you force them to keep going when they are self-weaning?
My eldest DS (5) was only breastfed for a month, because he was a very hungry baby and I couldn't keep up with demand! We combination fed for a bit but I was happy to give it up around 6 weeks.
If it works for you, great. If not, great! There's no rule, do whatever feels best.