What type of bicycle bell is easy to use with winter gloves?
I personally have found that anything with a lever that moves the internal clapper works best. Unfortunately, those seem to only come in large size.

Here's a photo of the one I have lying around:



I thought the spring in the internal mechanism had worn out which is why I wasn't using it, but now that I looked at it again it turns out it just needed a bit of oil.

Here's what the insides look like:



The clapper's attached to the lever with a spring so any contact with the lever won't dampen the clapper's movement.