DD2, who's about 20 months now, pretty well dropped her remaining, morning, breastfeed a couple of months back. Latterly, though, she's snaffled the odd very brief morning feed again and now, with Spring cleavage on display, she has taken both to groping around for a breast and, indeed, demanding 'booboo'- rather disconcertingly, as she's a late speaker and has never said this before. Once I've decoupled my rediscovered underwires she'll latch on, take a quick slurp on either side and then lose interest.
It's not particularly a problem, but I do vaguely wonder why she's doing it again (availability, I suppose) and indeed whether she'll go on ^for ever^....
My dd2 is the same age as yours and very passionate about "Milch" (her word for it) at the moment. I remember dd1 being the same at that age - a few months later dd1 lost interest and weaned herself. So there is hope! One thing I do is follow the "Don't offer - don't refuse" thing, and I try to distract her and only give in if she makes clear that she won't be distracted.
DD does this as well, although as she's a few months younger I'm not getting the verbal demand!
She climbs up on my lap and very pointedly starts poking at them until I get one out. Like you I've thankfully gone back to decent underwired bras, and it's a pita to sit there with one boob dangling free, being poked in the side by the dislodged cup just for 2 slurps of milk. Sometimes I can distract her by offering her a drink of juice instead, but when she's tired all she wants to do is have a quick drink, and then sit there and poke my nipple and laugh.
It's a good thing I've given up on any sense of dignity now, and no, we don't do it outside the house. Can you just imagine it in Mothercare?