Its odd to think that given that bones are non-specifically sized aside from weight, theoretically you could make a entire set out of the smallest creatures. Additionally, the OP might be onto something (sort of, though it's admittedly a bit of a silly post)
Fur carries off properties of insulation (that realistically means diddly squat from what i can gather in the game as current) as can be observed why yeti's don't immediately turn into abominable popsicles in sub-zero (not that this applies majorly to dwarves, though migrants arrive fully clothed). Though it'd be a lot of work, if bones were differently sized (/or just sticking to weight as a factor of size) and given individual material strength properties (helmet snakes for instance, and other hard-headed animals) it might just situationally buff up bone armour to be used in a specific way. (corpse piles can be divided up for butchers, with quantums for good measure)
One kestrel skull helmet given its small size (additional bones/materials or duplicate skulls needed) would be tough to crack but you'd need to probably farm them for enough to cover all your relevant dwarves not wearing very much, though kestrel bone would probably break really easily on chest pieces/greaves.
Throw on some helmet embellishments (little ribbons/bells, actual animal horns for goring as a side-skill that serve as another point to grab onto as a caveat, crundle and ram/bull/unicorn horns might see good use) and your bone brigade is good to go.