So I ordered a Clarke, the first ever mass-produced tin whistle and still one of the top brands. They're conical rather than cylindrical, which solved the problem of variable pressure nicely. They're famous for having "chiff," a desirable quality that I have no idea what it is. They're quiet, which is good for us apartment-dwellers. But the quietness brings another issue...
Imagine Pippin singing to Denethor, quiet, sad.
Home is behind, the world ahead.
And there are many paths to tread.
Pippin throws his arms wide like a diva and belts,
TO THE EDGE OF NIIIIIIIGHT,
Quiet and sad,
Until the stars are all alight.
The overblown (high) notes are twice as loud as the regular notes. AGH. I've been learning Pippin's song, and TO THE EDGE OF NIIIGHT is loud enough to turn heads in traffic. People have played these whistles for over a century, so there has to be a solution, but damned if I know what it is.
The good news is that I'm no longer afraid of the overblown notes. It's not as difficult as I thought to learn the point where the note jumps octaves. If anything, my problem is that I blow too hard on the next non-overblown note. So: progress!