My stick blender is wearing out, and for the
next one I want the smallest possible head.
That's so I can blend in a smaller container
and thus blend smaller quantities. Right now,
8 fluid ounces is about the minimum I can blend
without whipping air into the material being
blended. It's very important not to whip air in,
which rules out blenders driven by a motor from
below. Does anyone know of a stick blender
with a very small head?

I'd considered getting a laboratory homogenizer.
Some of those are like a stick blender with a
very small head, but even used on eBay they tend
to be rather expensive (hundreds of dollars).