Dear native speakers,
which is correct: they were sensible- sized dogs
or sensibly- sized dogs?
But don't use a hyphen with an -ly adverb. It's odd, but that's how it goes.
(I agree with the comment. I think those little dogs celebrities carry in their purses are not sensibly sized. If you can lose it in your couch, it's not the right size for me. On the other hand, if I lived in an apartment in the city, I guess a Bernese Mountain Dog might be too sensible either.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.