Update:

I bought the Halo airtight housings. Others were recommended, but none
were as cheap as the Halo ones!
(Only 8.xx at H.D.) Other airtights were around 15 a piece. Then, I
also got the Halo airtight trim (30WATH).
I think the trim piece is MUCH more effective at stopping the air than
the housing would have been by itself, and
maybe a standard IC would have been enough, but for an extra 2 bucks,
whatever.

I installed them, and can feel no drafts. I haven't wired them up
yet, because I forgot to buy wire. (I knew I forgot
something...)